A Guide to Troubleshooting Your Gas Furnace

No troubleshooting guide can cover every cause and solution for every gas furnace in existence. However, understanding the basic way a gas furnace works is a good start to diagnosing your furnace problems.

The first step in troubleshooting your gas furnace is to observe exactly what your furnace is doing – or not doing – and narrow down the possible causes. Often, you will find you don’t need a new furnace after all. Sometimes the simplest things can cause the biggest problems.

Inside a Gas Furnace

It starts with your thermostat. Your house is cold, the furnace needs to heat the house, and the thermostat begins the process. In general, your heating system follows a basic pattern:

  • The thermostat senses the house temperature and activates internal contacts that close the electrical circuit.
  • Closing the circuit signals the furnace to start.
  • Ignition begins. Older furnaces may use a standing pilot light while newer furnaces use an electronic ignition.
  • The gas flows to the main burners to heat up the furnace. Once it reaches the correct temperature, the furnace blower fan comes on, forcing air through the heating ducts and out the hot air vents, called registers.
  • The thermostat responds to the warmer temperature by opening the contacts, breaking the circuit. The fan will continue to run for a brief period of time – perhaps two or three minutes – to dissipate the heat remaining inside the furnace chamber.
  • The fan stops, the warm air ceases to blow and the thermostat waits for the temperature to drop again.

Of course, this is an oversimplification. To break down the complete process and explain every single part of the system would very complicated, and the repairs would be beyond the capability of the average DIYer. In addition, newer- and older-style furnaces operate slightly differently according to the type. At heart, each works in the same general way, however. Understanding the basics will help you identify the simple problems and solutions, possibly keeping more money in your pocket instead of going to furnace repair technicians.

Where to Start When Your Furnace Just Doesn’t Work

Sometimes your furnace doesn’t have any symptoms to clue you in to what is wrong. No smoke, no funny sounds or sparks. The furnace simply does nothing at all. It’s perhaps more frustrating than any other problem since other symptoms at least offer clues about what’s wrong. Quite often, however, the cause is something fairly simple. Troubleshoot the furnace by starting with the simplest causes and progress to more complex problems.

  • Check that your thermostat is set to “Heat.”
  • Is the thermostat’s temperature setting higher than the room temperature? Either double check the room temperature with a thermometer, or raise the temperature on the thermostat until you hear a click. If the room temperature is several degrees below the thermostat (allow a few degrees for thermostat inaccuracy) or the thermostat never clicks, continue troubleshooting the furnace.
  • Troubleshoot your thermostat. If you have a digital programmable thermostat, thermostat failure may be more obvious – the display is blank or flashing a code. Even older manual thermostats, however, can go bad or get too dirty to work. Troubleshooting your thermostat will likely take only a few minutes, so it’s a smart thing to check before admitting defeat and calling a furnace repair company.
  • Turn the fan switch on the thermostat to the “ON” position to check for power to the furnace. If it doesn’t operate, suspect either the furnace isn’t getting power or the fan motor, inside the furnace, is malfunctioning. If the fan isn’t working, heat will not come out of the heat registers, possibly making you think the furnace isn’t working even though it is.
  • Look for the SSU switch – formally called the Switch Supervisory Unit. Typically mounted on the wall near the furnace, the SSU looks like a bulky gray light switch box and features an “ON” and “OFF” switch. Check that the switch is turned on before proceeding.
  • Check your home’s breaker box to ensure the breaker that controls the furnace is on, or check the fuse box to make sure the fuse isn’t blown. Breakers, in particular, may react to a power surge by flipping the breaker to halfway between “on” and “off.” It’s obvious when this happens, as one breaker will be out of alignment with the others.
  • Flip the breaker off, wait two or three minutes and flip it back on again. Similar to a computer, sometimes simply resetting the power solves your problem.
  • Look at the pilot light. Is it lit? A standing pilot light should be visible when you open the combustion chamber door. If the pilot light is out, it must be re-lit, following the furnace lighting instructions precisely and observing appropriate safety procedures, such as turning the gas valve off and allowing the air to clear for several minutes. Have a professional light your furnace for you if you are not familiar with the procedure. If the furnace refuses to stay lit, consult a furnace repair technician.
  • Check the furnace gas valve to determine it is open. The valve will be located along the side of the unit, clearly marked, and forms part of the ignition system.

If, after checking every part and still not identifying why your furnace will not come on, consider calling a professional. HVAC service companies have special equipment and a deeper knowledge of your particular furnace’s inner workings.

Investigating Your Furnace by Problem or Symptom

Sometimes your furnace works, but it isn’t working properly. Troubleshooting the thermostat, power or gas supply is a waste of time – you need to jump straight to the problem. Take a look at exactly what is happening and, with a general understanding of how a furnace works, you can often at least narrow down the possible causes.

  • The furnace cycles on and off too often: Figuring out the cause of an overworking furnace may require a little investigation. If your home is poorly insulated and drafty, for instance, your furnace will work more. Another cause is an over- or undersized unit, which will also affect your utility bill. If nothing has changed except the frequency with which your furnace comes on, however, check the thermostat to see if it is accurate and clean. A dirty air filter can also cause the furnace to overwork, so check and change or clean it as necessary. Finally, the fan motor may have a problem. Consult a furnace technician for further assistance.
  • The furnace is extremely noisy: It may be annoying, but is it abnormal? Some furnaces are simply louder than others, with pings, roars and squeaks a sign of normal operation. Sudden and unusual sounds may indicate a problem, however. Many sounds are due to slipping fan motor belts or fan parts that need lubrication, as indicated by a high-pitched shriek or squeal. A poorly adjusted standing pilot light may emit a low, rumbling sound when the burners are off. With the burners on, the same sound may indicate dirty gas burners. If you hear a grinding noise, it typically indicates the blower’s bearings are shot and need replacement. Have a technician inspect the furnace and oil, adjust, clean or replace these parts, as necessary, to correct the problem.
  • Pilot light won’t light or stay lit: If the furnace is turned on, a standing pilot light will stay burning unless there’s a problem. It may be something as simple as the flame being blown out by a strong draft. Other possible causes include dirty ignition parts, air in the gas supply line or malfunctioning thermocouplers or flame sensors, both parts of the ignitor responsible for extinguishing the gas if your pilot light is out or will not light. Gas and electrical components are hazardous and you should never attempt to service the parts unless you know exactly what you are doing. Instead, turn off the gas supply and call a professional immediately.
    Once you complete your furnace troubleshooting and have your furnace working properly again, stay and observe it through one complete cycle. If the fan doesn’t operate as it should – not coming on, not going off, cycling too often – you may have a problem with the fan limit switch.

A useful diagnostic test at this point – or any time you suspect a problem with your gas furnace – is measuring the temperature rise across the furnace. Using as accurate of a thermometer as you have available, first find the temperature of the hot air in the heat register closest to your furnace, whether in the ceiling or floor, when the furnace is blowing heat. Insert the thermometer as far as possible and avoid touching the sides of the duct. Next, check the room temperature. Subtract the room temperature from the vent temperature to find the temperature rise. Compare your results with the temperature rise listed on the furnace data plate. While your temperature measurement is unlikely to be as accurate as one performed by a professional with sensitive equipment, an extreme difference between your temperature rise and the specified rise may indicate a problem. Possible causes include a dirty air filter, improperly adjusted burners, a fan issue or a problem with the fuel delivery. While replacing your furnace air filter is simple, most other furnace internal and electrical repairs are not as easy. Consult a service professional for further information.

Furnace Preventative Maintenance

Cleaning your air filter regularly will help prevent future furnace problems. Over time, your filter

collects large amounts of dust, hair, pollen, dead skin cells, nicotine if a smoker lives in your house, and other contaminants. As the filter clogs, the furnace must work harder and harder, ultimately lowering the efficiency and costing you more money. Most manufacturers recommend replacing your filter monthly, although pleated filters, considered high-capacity, may require replacement every two to three months. “Washable” filters, meant to be reused, may need servicing once or twice a year. Check your furnace filter requirements and change as recommended.

Once a year, inspect the furnace to ensure everything is operating correctly. Before the inspection, vacuum out and wipe down the area around the fan and completely across the outside of the unit. More advanced preventative measures include cleaning each fan blade with a toothbrush, if the fan slides out or is accessible, and vacuuming up the residue. Older furnaces may also benefit from a yearly motor port oiling. Just two or three drops of appliance-grade motor oil, added to the ports near the motor shaft, help keep the bearings and motor running smoothly. Consult a service professional for more information and assistance.

Even though it may seem unrelated, proper home insulation levels and winterizing measures you can do yourself impact your gas furnace as well. No matter how new or efficient your furnace, it simply won’t keep up in freezing temperatures when the home isn’t weatherproof. Another problem is leaky duct work or poorly insulated ducts running through unheated areas such as the attic or crawlspace. Consider consulting a home energy audit professional or HVAC repair company to identify trouble areas in your heating system and home. Remember, an ounce of prevention is worth a pound of cure!


Kim - February 16, 2015 at 2:19 pm

We have a 2007 Bryant gas furnace. For the past three years when the temp outside drops below 20 degrees it quits working. When the temp is above 20 degrees it works fine. We have had someone look at it twice and both times they looked at it and said that it was fine. That’s a lot of money for no resolution!
What could be the problem?

Merriah - February 15, 2015 at 9:21 pm

We have been living in this house since 2010 and they said the furnace was new but this year the furnace has had a high pitch squeal and is constantly turning on then off for a second then back on. Our gas bill is tremendously higher this year. Also we can not get our house above 69 and we have even set the temp to 75. Our house is freezing this year. I have turned on the oven and baked just to warm the house up. Any suggestions? We have a home warranty but wondering if it is something we can fix instead of calling and paying a $75 dollar fee to have it looked at. Thanks!

Maghan - February 4, 2015 at 12:05 pm

In my apartment I have BDP furnace, which 20 years-old.
Recently it started to make a strange, extra loudly sounds.
I am not an expert at this, but for my it looks that I have to switch 115 volt 395 inducer motor- complete kit.
How unsafe is the furnace when runs like this? Can it explode or gas leak? it is natural gas furnace.
Can I switch this part by myself or need to call professional?
Thank You

PatPro - February 8, 2015 at 10:47 am

Normally your furnace will not run if the inducer (combustion) fan will not run. The inducer fan proof-of-flow switch in the gas valve will shut itself down and not run. It might light off, but not run for any length of time.
Is it unsafe……..well….yea. That’s why it is something the gas valve proves is operational before allowing ignition. It probably won’t explode but who wants to take that chance. And yes, you can make the repairs easily.

joseph - January 31, 2015 at 6:41 pm

I have a new gas fired Boiler (3yrs) and new thermostat, but when I turn the thermostat to 80 , the room temperature gauge will not go above 70 , why? (the room stays very chilly). What could be the problem?

joseph - January 31, 2015 at 11:46 am

I have a new gas furnace (3yrs) and new thermostat, but when I turn the thermostat to 80 , the room temperature gauge will not go above 70 , why? (the room stays very chilly). What could be the problem?

Michelle - January 31, 2015 at 11:09 am

My furnace is a miller 80. It stopped working 4days ago so I bought a new igniter but it didn’t fix the problem. It comes on and runs for a minute but shuts
back off. It’s 6 years old. Any suggestions.

Jim - January 31, 2015 at 3:35 am

Hi…I replaced in igniter a few years ago. The repairman was sure I needed a new ignition board, because I guess igniter past his meter-test,but then when he pulled it out it was broken. Now we have a cold snap happening and once again have heater problems! Once again the repair man says I need a new ignitor board ( an older Fenwal that is not easy to find: 05-212226-103) and the replacement is going to be tough to use unless someone has the wiring harness.. As soon as the stores open I will start looking for any new ignitor and a new board. Question i have now is why I suddenly can’t manually delete this furnace anymore. A couple times after I got it lit, the igniter did kick on and work. it showed symptoms of a failing igniter rather than a bad board. But now when I try to manually light it, the gas starts to flame up but then the gas cuts off.ames start and then the as cuts off…throughout the night I was able to manually light it and I even saw the ignitor kick on a couple of cycles!. So I don’t think it’s the board although I will replace it just to have it. Now all of a sudden even if I try to manually late the gas it doesn’t hold any kicks off and its not asking for gas. 511-330-184 ignitor.

Jim - January 31, 2015 at 3:37 am

…well it looks like autocorrect has made this kind of difficult to read. I want to light the furnace not delete it… Sorry

Bec - January 30, 2015 at 9:30 am

My high efficiency goodman gas furnace is 4 years old. Last year, when it was three years old, it started vibrating one day when the blower came on. Over time the vibrating got louder and more violent and has been shaking the electrical loose regularly. So far my trouble shooting suggests that there is something wrong with the blower fan bearings, belt, or motor.

So I have two questions: first, how do I determine where the problem actually is? And second, why would a well made furnace develope a big problem when it is so young?

There is a little more information that might have to do with the second question. I was going to sell the house so the prospective buyer (an HVAC guy) had an inspection. When I returned home after the inspection is the day the vibrating problem began. Coincident? I figured it would become the buyers problem and not a big deal for him since he is in HVAC. Anyway, the deal fell through and I’m stuck with the problem. But I wonder if maybe he “inspected” the furnace in a way that could have caused the problem with the blower?

Lin - January 10, 2015 at 7:52 pm

I live in a house with a gas furnace that is probably as old as Jesus. It has a pilot light, and has never had an issue over the years until this week. It will keep the house nice most of the day.. I keep it about 62-65, but about 20 minutes ago, the pilot light has gone out for the 3rd night this week. My son can light it back when he’s home in the morning, but its going to be a cold night until then.

None of the heating and cooling services will touch this old heater, so I can’t find anyone who will properly service it and clean it. I personally can’t get to it to light it. I know I can’t afford to have one of the new heating systems installed.. I can only guess they would need to replace the duct work as well.

Does anyone know who to contact to work on ancient heaters?
Does anyone know the ball park of a new heat system?

joshua - January 17, 2015 at 7:33 pm

Lin hi depending on the size of your house you could get a 95percent efficient furnace around onethousand dollars and that is the 150000btu smaller one around eight hunderd easy to install and hook right into your old duct system. Look around call diffrent places that sell them but by on bigger than the sqaure footage of your house so it doesn’t have to run hard all the time. Your duct system does not have to be updated just modified at the plenum for the new furnace. Meaning in english bending new metal from the furnace you buy to adequate your existing duct..

MARIANNE LACKEY - January 18, 2015 at 10:14 am

Lin: My parents have had an old floor furnace (gas) ever since the house was built in 1948. We have never had a problem with it. Sold it a couple of years ago and understand it is still running strong! Cheap! Cheap! Cheap!! Most people today, of course, don’t care for the floor furnace because it gets hot to the touch. I had two younger brothers at that time, and they were taken over by the heater and shown that it was hot and told not to stand on it nor put anything on it. Kids back then minded their parents better, I suppose, but we just never had anyone get burned, etc. I think my Dad crawled under the house every year and checked it out for safety. He would take the grate off from the floor and I would lean down and light the pilot. Other than that, he may have replaced the pilot light thingy if it wore out or became hard to keep lit. Good luck.

Frank - February 8, 2015 at 1:28 am

Usually a pilot light that keeps going out us due to a faulty thermocouple (the little wand in front of the pilot light). I’m surprised no heating contractors would check it out, as a thermocouple is a piece of cake to replace (basically a service call, and they should have the part — which costs about $10).

I’ll grant that many may want to strong-arm someone into getting a new one, but not all contractors are so mercenary. And most old units are very simple, with parts that could be retrofitted if something like the original is not available, though such work tends to be on the expensive side — at least the first time for a certain repair.

I would do a lot of internet searching using phrases such as “old furnace repair (your area)” or “gravity furnace repair (your area)”.

A new furnace would typically run at least $3000 for a small house, though you might get a better deal in spring, as I did. If you have good credit and a steady income you may be able to get one financed, in which case the heating cost savings might just about balance the payments over the course of a year if the existing furnace is very old and inefficient.

As Joshua pointed out, the ductwork wouldn’t need to be changed much, only very near the unit. If a contractor tried to buffalo you into paying for extensive ductwork or wiring, cordially show them the door. They may need to put in a chimney liner for the water heater, though, even if the new furnace doesn”t use the chimney.

Hope this helps.

Jeanette - January 3, 2015 at 9:51 am

Hi, We purchased a Cedar Ridge Hearth vent free gas wall heater Model #MD3TPU. My concern is the pilot light makes a crackling noise (bacon frying) all the time and it wakes me up at night because it is placed in the hall next to our room door. My husband doesn’t seem to think it’s out of the ordinary but not me. I believe I have never heard one make such a noise and be so loud. I want him to take it back but he doesn’t want to fool with it. Can it be fixed or could it cause health problems leaving it this way?

Leann - January 13, 2015 at 10:36 am

I would take it back and exchange or at least call the company. I have two but different brand, they are very quiet.

NIKKI - December 31, 2014 at 3:33 pm

I have a older thermostat and my problem is my heater will run for like 5 min. Maybe 10 if I’m lucky and then it kicks off for about 5 min. And right back on. It keeps doing this and it is going to make my bill go threw the roof. I’m gonna go outside and flip the breaker and see if that helps. I’ve also turned that little nob where it starts out on .18 to .9 mine was set on like a .7 i turned out down to a .3 and it isn’t kicking on as much but it don’t run but a few min. Any info i would greatly appreciate.

Carie Kendrick - January 15, 2015 at 7:33 am

We live in WI, and our furnace does this during real cold spells. It’s usually this pvc breather pipe that collects condensation (about a cup or more of water) fills the bottom of this pipe. It has a rubber end with a clamp at the bottom of it. We took that off and drained the water out. The problem went away.
Our Heating guy found that problem last year; and we do the above whenever that starts to happen.

Kay Johnson - December 31, 2014 at 11:25 am

Why do my heat comes on one day but doesn’t stay on all day. Some. Days it just won’t come on. I tired my heat on 80 with and without the fan on and its still come on when it want to.

Michelle - December 25, 2014 at 9:11 pm

My heater won’t even turn on. I turned the temperate way down and turned the braked off for a few minuets then back on and the temp. Up-it still doesn’t turn on (it’s so cold and on Christmas

brent hewitt - December 23, 2014 at 12:51 pm

i have a gas fired furnace that wont come up to temp in 1 zone (2 zone system). when i turn the thermostat off/on it kicks on and gets up to temp. the thermostats are newer and all the relays are workign fine. when i go to bed the temp never gets below the lower temp setting at night but in the morning it wont reach the higher day temp, it stops 2-4 degrees prior unless i turn temp off/on again

William Peters - December 22, 2014 at 8:24 am

I have an old miler natural gas furnace with hot surface ignition. I replaced the gas valve the control box the transformer the limit switch the fan relay the inducer motor and the blower motor there is only the fan limit switch and 24 Volt RBM Blower Relay (SPNO) (4-Terminals) which I haven’t changed. the inducer will turn on for about a minute the ignitor will glow nice and red then the gas valve will make this weird very short buzzing sound then the ignitor will then go out but the inducer will continue until I turn the uni off. and yes it has gas my stove and hot water are still working fine. the furnace model number is CMF80-PG-DI-N it was originally propane but was converted some years ago to natural gas. Can someone please help otherwise I have to save up to get a new furnace and by the time I save enough my pipes will have frozen.

Thomas Bo - December 19, 2014 at 5:29 pm

Have 2 floor furnaces. The pilot light does not go out. Work fine for a while, then does not kick in when thermostat is turned up or just stops heating. Can step on it and sometimes kicks in. What could it be? They are like 10 years old.

Tye Bennett - December 18, 2014 at 12:59 pm

I have an old gas furnace with an intermmitent pilot. It’s over twenty years old and needs to be replaced, but I don’t have the money at the moment.
The problem is it will come on for a whole cycle then shut off. When the next cycle kicks on it won’t light. If I turn off the power for a bit it will do the same thing, light for one cycle then not light for the next.
What are some things I could check?

Lisa - January 8, 2015 at 2:14 pm

What did you find out about this problem?

brian - December 9, 2014 at 5:47 pm

our furnace wont run unless i take the door off then put it back on then it will run till it stabilizes but then wont run agian, untill i do over again. what is the problem

Ron - December 10, 2014 at 11:06 am

Sounds like a bent door or bad door switch

Arash - December 9, 2014 at 9:20 am

when the thermostat is set on heat just blows cold air No flame,when is set on emergency heat it works normal with blowing air and flame,do you have any idea why?
is it ok to run the natural has furnace on emergency heat?thanks

hdidi - January 7, 2015 at 5:23 pm

I’d like go know the same

Kylee - December 8, 2014 at 6:16 pm

I had a brand new thermo pride gas furnace installed in May 2012. Winter of 2013 and again this year, the furnace kicks on, then shuts off before blower comes on. Does it three time then does not come on again for hours. I’ve had it looked at a few times. What the problem seemed to be, a water puddle in the burner box. Unsure of how this is happening unless it is getting blown in from air intake on roof. Soaking up the water was helping, would work good after being put back together. Tonight, it quit, I opened up the burner box, dried out out, furnace kicked on, then shut off. Waited about 45 mins, turned thermostat the whole way down and then back up, it kicked on and worked. And now again, the furnace kicked on, went off, kicked on, went off, ….. 3 times. Any ideas/suggestions??

Nicole - December 5, 2014 at 6:00 am

I have an older gas furnace in a house I recently purchased. I replaced the filter (16x25x1). When I took it out it was very bent horizontally in the slot for it. I have replaced it with high quality, lower quality and fiber glass filters. When any of these are placed in the furnace the furnace rattles very loudly when it kicks on, it will rattle during the whole cycle. If the old one is placed back in, it will be quiet but it is not tight against the opening. I’m lost on the cause. Anyone have suggestions?

Dan - December 17, 2014 at 12:47 pm

Try a larger filter…the previous homeowners may have installed the wrong size filter..

Ted - December 3, 2014 at 2:40 pm

For the last several heating seasons our gas furnace will work fine for days and then it stops. All we do is go to the breaker (which is NOT tripped) and flip it off and back on again. The furnace runs again for a day or two then we repeat the whole thing again. Im afraid that one of theses times it might not turn back on. Any Suggestions ??

Yvonne - December 23, 2014 at 9:06 am

Ted, did you ever find out what the problem was? We are having same issue with our recently purchased retirement home – except electric Central Air / Heat unit. No tripped breaker but if we go out and flip it off and back on the unit will work again. Happens with both heat and air.

ted - December 31, 2014 at 3:19 pm

When you go outside and flip the breaker your resetting it. So something is causing it to do this i do not no what. But i do no that when you flip that breaker to the heater your resetting it so it will work. I could be wrong but i have learned that flipping the breaker your resetting it. Hope that helps on why it will work again for a day or two.

Red - January 5, 2015 at 8:59 pm

Having the same issue. I’ve had to “trip” it twice now. Think it may be a bad relay. Calling furnce guy tomorrow. With-18F, & kids & pets, dont need it NOT coming back on one of ghese times. Hoping nothing major or expensive. 🙁

Gary - November 27, 2014 at 11:09 pm

what would make your furnace make a clicking noise while its running then all the sudden it just stops. I got to have my thermostat 72 or in between 72 and 71. it just started doing it a new days ago but it doesn’t doo it all the time and I don’t know what is causing it or what the problem may be. I’m hoping someone could please help me out on telling me what to do. I’m to the point where I’m about to call someone to come out and check it out

Gary - November 27, 2014 at 11:23 pm

it only does it while its on and can someone please help me. I’m losing my mind with the clicking noise. its not real loud but it only does it while its on. but it starts up real good and shuts down fine. but like how I said it just started making a clicking noise. I clean and replace the fitters at the 3 times a month soo that y that its okay. then If they are dirty I run them under cold water and leave to air dry be4 putting it back on the furnace door. then if it runs for a few days then all the sudden the clicking comes back for about 15 mins then stops

chris - November 23, 2014 at 3:38 pm

I have a 7 yr old ruud 80% upflow furnace. Getting a lot of return air leaking into the burner chamber and causing flame rollout switch to trip. What is best way to seal this. Was thinking mastic but not sure if it will handle temp

Kelly Wanberg - November 23, 2014 at 12:38 pm

I have a Lennox Pulse furnace, it makes a sound like a timer, then there is click sound, it tries to start then nothing happens. It does this repeatedly. I picked up a used ignition control switch for it and it started working again for awhile but now it is doing the same thing. Baso makes new switches for the Pulse furnaces, would that be a option or is there another problem?

Sherry - November 19, 2014 at 6:54 am

My furnace won’t kick on until it is 6 degrees below the set temperature, is there a way to get it to come on when it’s only 3 or 4 degrees below the set temp?

If anyone can help, please let me know.

Danny - November 20, 2014 at 8:30 pm

Probably not, though it would depend on your thermostat/furnace type. All thermostats are designed to have a certain difference between the set target temp and the time it initiates the furnace to allow it to run long enough to be efficient, otherwise it would cycle on and off far too often to operate as it’s designed to.

Think of it like this, if it’s coming on when it’s only 3 degrees below the set temp, vs 6 degrees it will have to come on roughly twice as often for half as long, and that burn time may not be long enough to efficiently get the furnace chamber and all the HVAC plumbing heated up in your home.

If you’re feeling like a 2 degree difference is making/breaking your comfort level, I’d say your best bet is to just bump the setting up by about 1-2 degrees. I’m guessing you’re set somewhere around 65-68 and you don’t like the way it feels when it’s going down to ~59* (which means the less efficient areas of your house are more like 55*). The 2* bump in the top end to ~70 won’t bother you at all, honestly you’ll hardly notice a difference between 68-70, and it effectively does the same thing to the bottom end temperatures as the thermostat kicking the furnace on earlier, it’ll kick on 2 degrees sooner 😉

It’s going to cost you a few more dollars a month to do it this way, sorry there wasn’t a better answer :-/

Duane - November 21, 2014 at 9:00 am

All thermostats have what is called an “anticipator,” or some type of delay mechanism. It sounds like the delay setting on your thermostat needs to be to shortened, to allow the furnace to cycle on and off more often.

Frank - December 16, 2014 at 1:23 pm

Look for a movable metal lever inside the thermostat. Your RANGE SETTING is way off. My thermostat is SET at 68 deg. When the thermometer next to it reads 67.2 the thermostat opens up the gas valve. At 68.8 the gas valve closes. So a RANGE SETTING of +/- 0.8 deg. F, and that’s what you want for comfort.

hdidi - January 7, 2015 at 5:26 pm

What do u do if it’s an electric thermostat

Rusty - November 18, 2014 at 10:19 pm

Hi we have a 2003 Carrier furnace. We have replaced the fan, control board, high limit switch as well as the gas valve, inducer motor and wheel. Filter is changed every month however, if you change temperature of home more than 1 degree it trips the high limit switch because of overheating. It’s a two speed furnace, I’m frustrated please help.

chris - November 17, 2014 at 7:19 am

i have a diplomat natural gas furnace i can only get the heat to kick on when the thermostat is in the on position and not in auto how can i fix this

Ron - December 10, 2014 at 11:10 am

Check thermostat

Eugene - November 16, 2014 at 7:37 pm

I have a old furnace. When the burners light the first burner lights with a good bright flame but the next two burners wil light with a poping sound and some times it will blow out the pilot light. when the burners do light the first burner has a strong full blue flame but the last to burners have a small weaker flame. What is the problem?

Susan - November 16, 2014 at 2:24 pm

I have a beach house. When I got here last night it was 115 degrees in the house. Yet the thermostat reading was set to 60 degrees. What would make the Lennox gas furnace pump out heat like that. Turned off the furnace at the electrical box.

Concerned at how long that was on and what might be ruined in the house.

Josh Wilcox - November 16, 2014 at 2:03 pm

The managers of the trailer park I just moved into have just installed different used gas furnace into my trailer. When I light the pilot light and the furnace runs for a while it will all the sudden pop (like there is an explosion in the furnace) and it blows iut the pilot light. The managers and maintenance guy said its dust blowing out and it will stop doing it once tye dust is all out but it scary at night to sleep thinking that when this happens you can smell the gas. What could be causing this?

Elliott - November 25, 2014 at 10:26 pm

You can smell gas for a bit because the gas still comes out until the thermocouple gets cold enough to shut off the valve. If it is dust then they should blow it out, but it’s also possible there is a inconsistent mixture of gas and air. They should have a professional check it out if it keeps happening. It’s ip to you if you trust them enough to take a chance. I would say that unless you hear gas coming out when the thermocouple is cool, that you probably shouldn’t be worried about the smell so much, but I’d have to be there to tell you what’s actually happening

Dave - November 16, 2014 at 1:19 pm

I have a kenmore power miser 70, my question is my pilot will light then the main burners will light, they stay lit for 1 1/2 minutes then everything goes out for 35 seconds, then they re-light for 1 1/2 minutes then goes out for 35 seconds and so on and so. I timed it and it did this faithfully for like 10 cycles until I got tired of timing it. so my question is ” should the burners burn constantly or is this the normal?” if it is not normal what could the problem be? it is getting really cold and I don’t want to lose the furnace all together

Renee - November 16, 2014 at 10:33 am

My 10 year old furnace had the blower motor replaced last spring. Since the installation ( by a furnace technician) my furnace functions like this;
It is receiving signal from the thermostat
It fires up but shuts down without the blower coming on.
I remove the fresh air intake pipe, and it works fine? The minute I place back the fresh air pipe to the furnace, it doesn’t fire up again. So I used a snake to determine if there was a blockage in the fresh air intake. Other than a bit of dust, it was clear. I wonder if it is not good to run the furnace with the air from the basement instead of outdoors? This is very strange and I am hoping somebody else may have experienced this?

Thanks in advance

Linda threadgill - November 15, 2014 at 6:40 pm

I have an old central heat unit which is about 35 years old. I can light the pilot light. After that it doesn’t do anything. What do I need to do?

Vilonda - November 15, 2014 at 7:37 am

When I turn my heat on, the furace will come on heat my home to the desired temperature and cycle off. Once the temperature of my home starts to drop, the furnace does not cycle back on, but I can hear the furnace buzzing. Could my problem be the thermostat or is it the furnace?

Ty - November 14, 2014 at 11:42 pm

my furnace has worked fine and is only 3 or 4 years old. i came home from work the other night and i noticed it was cold in the house. i checked the temp and it was at 68 instead of the 70 i have it set at. turned it up to 72 and it didnt kick in changed the batteries in the thermostat and it kicked in and worked fine. well now 3 days later its doing the same thing. i take the batteries out and put them back in and it starts to work. any solutions on this problem as its very cold in Mn atm. thank you

Danny - November 20, 2014 at 8:39 pm

Furnace seems fine, I think you may just have a bad thermostat. If you personally had it installed, you may want to check you warranty as it may still be covered. If not, it may just be $20-$60 for a new digital thermostat unit that you can find at any home depot/Lowes store. They’re generally pretty standardized and even use the same wire colors for the most part, but check the model of your furnace to see whats compatible.

Also, if it doesn’t fix the issue, you can always return the thermostat to the store, just don’t destroy the box when you open it.


Nikki - November 14, 2014 at 10:55 pm

Hi, my furnace is about 15 years old. It is gas and I turn on the furnace and it will ignite and then the flame goes out. I think it’s called short cycling constantly. I had a repair guy here last week and he replaced the ignitor and it worked good for a day or two and now it just does the short cycle. I have replaced the filter and installed a new thermostat that’s programmable a few weeks ago. Does anyone have an idea what the problem could be? Thanks

Sham Persaud - November 21, 2014 at 2:08 pm

Your flame rod (flame sensor) may be dirty and may need to be cleaned or replaced. The flame sensor usually have one wire attached by a spade connector. It usually held in place in the combustion chamber by a 1/4 inch nut. You can remove it and clean it with steel wool and reinstall. The flame sensor senses the flame and tell the gas valve to stay open.

Jonathan May - November 14, 2014 at 3:40 pm

My gas heater for my house is acting really funny. The automatic gas valve went out. Got it replaced. Worked fine for one cycle. Went to check it before bed and now only the pilot light lights (auto light) and it stays burning but the “jets” never fire off. Like no gas is all of a sudden getting to it. I have checked continuity on all sensors and they all have that. Any ideas?

Jenny - November 14, 2014 at 12:04 pm

We have a Goodman furnance for the last 7 years . It works great if the weather outdoors isn’t real cold . The last couple of nights we havebeen in the teens and I set the the temp. in the house on 70 . It will go to 70 but I noticed that the fan keeps running I have to get up and change the the thermostat down for a few minutes then turn it back up , the fan will shut off . During the day there are no issues , the fan turns on and shuts off like it is suppose to do . My question is , why is the fan running and running all thru the night ? We have a new digital thermostat and my husband always changes the filter .

Catherine - November 13, 2014 at 11:08 pm

My furnace is cutting off before it reaches the temperature on the thermostat. It will usually start to work again after I play with the thermostat for a bit turning it off and on and turning the temperature up and down. I have a window air conditioner and there is a lot of air coming in thru the air conditioner and window. Could this cause the problem with the furnace? As the fall approached when it was warm during the day but colder at night there was no problem with heating the house, only now when it’s really cold outside.

Ken - November 9, 2014 at 10:12 pm

Can just one speed go bad on a multi-speed Motor? I just replaced the multi-speed blower motor on a Lennox furnace. After a few days it started making rattling noises just on the 1st stage low speed, then the low speed just quit. I suspect that I have a bad motor or controller? Is that possible? Thanks!

Bella - November 12, 2014 at 7:31 pm

With the power off, can you spin the blower wheel easily? Is it binding on anything?

Sam - November 9, 2014 at 9:05 am

My furnace is in my attic. The furnace only turns on in the afternoons when the attic is warmer. Once the sun goes down and the attic cools the heater does not turn on. I have had a repairman here three times. Of course the heater works when he is here. He has replaced the thermostat and can find nothing wrong with the heater. It does not work at night when it is cold outside. Any ideas are very much appreciated.

Bella - November 12, 2014 at 7:12 pm

is there condensation or rust on the inside of the furnace?

Gail Gardner - November 13, 2014 at 11:12 pm

If you use propane it can act strangely when the weather is below freezing. Pilots may go out or stoves that have igniters will refuse to light unless you use a match or lighter. Search for “propane tank freezeup” for more details. I believe there is something that can be added in the winter to prevent this. I suppose that an igniter could also be flaky so that it only fails when cold.

June - November 9, 2014 at 4:43 am

My gas heating has an intermittent problem. Sometimes it works well for weeks,then suddenly the water is not heating,and radiators are only working to about 20% capacity. I have had about 20 call outs from maintenance but can’t seem to get to the bottom of it. Would it be possible water in the system is dirty? Many parts have been changed. When the breakdown happens,just have to flick a switch and everything works again. I am going to rent out the apartment, so the issue has to be resolved urgently. Any advise?

Robin - November 8, 2014 at 3:42 am

With the rubbling sound I watch the ducts vibrate this is scaring me I am afraid of my furnace exploding please help me I am very worried for my family

Bella - November 12, 2014 at 7:02 pm

change your filter

Robin - November 8, 2014 at 3:37 am

Hi I have a Lennox furnace the original in my house that was built; in the 1970′s well I turned on the heat and got an awful rubbling sound and the furnace was running very hot what do think it can be

Jeff - November 7, 2014 at 11:22 pm

My gas furnace only works when I turn my fan on manually. When the furnace kicks of the fan keeps blowing. The fan will not shut off unless I manually shut it off. I cannot pin point the problem.

Bella - November 12, 2014 at 7:09 pm

What kind of furnace? It’s either the fan control/limit or the control module (circuit board)

Jonathan May - November 14, 2014 at 3:48 pm

Bella total off subject of this post but I didn’t know if it would alert you that I replied to this post or not. You see to have answered a lot of these questions. I posted above and really need to find a solution to my issue. I have paid repair people to come look and they can’t seem to figure out the issues. Thanks in advance.

Jonathan May - November 14, 2014 at 3:49 pm

I’m not trying to rush anyone. Only real issue is that it’s going to be 30 degrees here tonight and I have 3 kids. Just really worried about them. It’s going to drop to 24 in a few days.

Parashar - November 1, 2014 at 1:36 pm

Natural gas high efficiency furnace does not work with Auto setting,but furnace works fine with Fan “on” position. What could be the problem? Pls let me know asap.

Tom Hastings - November 1, 2014 at 8:10 am

Also check fuse on circuit board inside furnace (mine was 3 amp) if furnace doesn’t start at all, in addition to the great suggestions given above.

Howard - October 22, 2014 at 7:22 pm

When I turn my thermostat up I can hear it click but nothing happens Its an older furnace with a pilot light.Its done this before and all of a sudden it just started working.

Bella - November 12, 2014 at 7:06 pm

dirty thermocouple, clean it or replace it.

Darrel - October 18, 2014 at 9:24 am

My son rents a home that has an older gas wall furnace, made by Sears. The problem is it won’t shut off. It will keep running much higher than the thermostat is set for, and the little house gets extremely hot. We have replaced the thermostat on the wall. I just ordered a thermocouple hoping that may be it. I am not sure how old it is, maybe 20 plus years old. Anyone have any others ideas I can try before the part arrives? Thank you!

james - September 23, 2014 at 5:31 am

my 30 year old gas furnace will heat up the house to 20 degrees Celsius then shut off, if I turn the thermostat down to zero wait 1 min then put it up to 30 degrees the furnace will start up and run up over 20 degrees. any ideas what the problem could be?

Mayur Jain - September 8, 2014 at 6:35 pm


I recently switched my bryant 90 plus furnace from propane to natural gas. The kit was essentially orifaces/jets. The issue is that the furnace would not lit up. My plumber said as the outside air is warm, the furnace is getting confused to kick in heat or not. I am not cconvinced at all. He also said there is a thermostat outside which is sensing outside temperature and the furnace is more confused. I am really worried if my plumber knows anything or not. Any suggestions/help really appreciated.


Bella - November 12, 2014 at 7:29 pm

that outdoor thermostat is most likely for a whole house humidifier or just a convenience thing maybe telling your thermostat the outdoor temp. A furnace can run regardless of the outdoor ambient temp. When you turn the thermostat up and heat on, does anything happen? If the inducer and the blower turn on and run continuously then you most likely have a open limit switch. The furnace thinks it’s overheated and trying to cool itself off. If just the inducer runs then your pressure port/hose could be clogged.

bhush - June 18, 2014 at 11:52 am

I have goodman furnace installed recently. its 94% high effeciency furnace. From day one i am having this problem. unfortunately the contractor is bankrupt & closed his business.
Issue is the ignitor lits, but flames does not comes on. I can see the door cover gets sucked in (looks like due to vacuum). Work around i did was taking off the combustion air intake duct from the unit flange and everything works fine. Same happens if i open the furnace door flame compartment, normal operation.
Can you help me to understand possible causes.

Bella - November 12, 2014 at 7:14 pm

blocked or undersized fresh-air intake. Make sure nothing is blocking the outdoor PVC pipe.

Aaron - April 27, 2014 at 3:17 pm

The last couple of months or so now my gas furnace has been intermittently blowing cold air and often in the middle of the night where, we wake up and it is cold in the house but the furnace has been running since the malfunction happen (motor is very hot to the touch). I have noticed that when the furnace is operating normally, the flame seems to fan out and then it blows hot air, but when it is “acting up”, the flame is lit, but is not fanned out like it should be, and the furnace will run forever unless I (Reboot the system) turn off the the thermostat, go down stairs, turn off the gas, then go to the breaker box, cut main power to the furnace, wait a couple of min. and then turn power back on, then the gas, then turn on the thermostat, then it blows warm air correctly until the next time it decides to act up again. Any ideas? The furnace was installed in 1998, it is a Heil furnace & I change the air filters regularly, but do no other maintenance.

jeannie - July 11, 2014 at 5:56 am

That blower motor will stay on to cool the HEAT REGISTER down if overheating Its a protective mode so Furnace wont catch fire. Mine kept running and sending up COLD air and NOT enough warm air and it was diagnosed as needing a NEW HEAT REGISTER since the Old one was rusted (i saw old removed) It cost half as much as a new furnace with labor due to it was an Emergency Visit cost, because it happened in the middles of winter on icy cold day. The emergency visit labor was 130.00 just for coming out (regardless if fixing nothing) and 175.00 per hour to change part that costs 500.00 BUT SO JOB was $1,350.00 And one month earlier the blower motor had failed (due to on more often) and had been replaced NOT knowing that the Heat Register was on last leg. and Its most likely that buying a new furnace when a major part goes is best since there are other components with wearing parts and we already spent the amount of a new furnace so far.

Alex - October 4, 2014 at 11:05 pm

When i turn on my gas furnace it works and blows warm air for a little while and then just blows cold air and constantly runs. then I have to shut it off for about 20 minutes then turn it back on and it works till it does it again what should I do and what is the cause?

Stacy - February 28, 2014 at 1:20 am

My furnace kicks on fine, pilot ignites, everything works except when the blower comes on it doesn’t blow hot air anymore just blows cold even though there is a fire and the smoke stack is really warm, This started about four days ago and it’s now – 25 below outside and I have no heat! Please, any help would be appreciated!

Hector Gonzalez - February 21, 2014 at 6:00 pm

I purchased a home that had an older trane furnace on the lower level. Everything operated fine until the day I changed the thermostat. Now it occasionally fails to light the pilot but the fan still kicks on and blows natural gas throughout the house. This scares the heck out of me and I purchase an explosive gas detector. I cannot afford a new furnace right now but a furnace company tole me that is what I needed.
I tried cleaning the grill closest to the pilot but cannot seem to remove the pilot extension piece to clean that out. could this be related to changing the thermostat or just coincidence? Could changing the thermocoupler help this problem?

Hector Gonzalez - February 23, 2014 at 3:07 pm

So i managed to remove the entire pilot assembly , and cleaned it really good. So far it seems to ignite much more consistently. Things I noticed while I had it apart playing with it are a) The pilot valve stem was seriously corroded b) pilot spark was attracted to the flame sensor 75% of the time. So I adjusted the pilot to be closer towards the pilot light figimabob, and I cleaned the pilot valve tip thoroughly. Now it fires in the right direction and actually lights the pilot before the grills fill up with gas for a much more consistent ignition process…. Any tips on what else I can do to make this thing last a few more months without dying is still very much appreciated

Hector Gonzalez - February 26, 2014 at 5:57 pm

turned out I had holes in the heat exchanger… 🙁

Mj Fackler - February 14, 2014 at 2:37 am

We just purchased a single-story slab on grade open floor plan home, and the heat runs off of propane so it is gas. The problem seems to be that when the cycle is running (heat kicks on to warm the house)
There will be a popping noise coming out of the living room vent, and it pops just about every minute until the cycle is done. Does anyone know what this could be?

Troy shire - February 16, 2014 at 5:11 pm

Could be something in the furnace. But most likely your duct is expanding making a popping sound.

Pearl - February 12, 2014 at 1:53 pm

Problem is that the thermostat is set to 69, furnace will not come on sometimes till it gets down to 62 or if I play with the thermostat to get it to turn on. Then it will run the way its suppose to until the next day or so. We had 3 different guys come out only to tell us they can not detect the problem unless they are here when it happens. Any ideas what could be the problem?

Jim - March 12, 2014 at 5:25 am

I have been having same issues, did you find anything out? Any help would be great.

Ralph - March 23, 2014 at 1:45 pm

I just replaced my thermostat, it was having similar irregular issues. Was only about $50 at Home Depot and was an easy DIY fix.

jeannie - July 11, 2014 at 6:13 am

There is a DIP SWITCH on back of wall thermostat. If removed from wall SEE on back and find settings. The setting dip switch (Either Up or Down) for STEAM HEAT since the Steam Radiators are still giving off heat even after the furnace shuts down. The “HEAT PARTICIPATOR” is a setting for shutting off the furnace before it gets up to the desired temp setting, since it would go way UP above that after the furnace shuts down, if allowed to stay on. Forced hot air doesnt work this way so that why the setting is there. Any furnace guy who doesnt know this is spooky or not honest. Instructions are on back of a new thermostat – Home Depot average cost 50.00

jeannie - July 11, 2014 at 6:28 am

Correction of TYPOS same reply:
On back of wall thermostat there is a DIP SWITCH. Maybe only 3 pins. When removed from wall SEE on back and find settings. The settings of Dip Switch (Either Up or Down) is due to that STEAM HEAT Radiators are still giving off heat even after the furnace shuts down. So the “HEAT ANTICIPATOR” is a setting for shutting off the furnace before it gets up to the desired temp setting, since the actual temp would go way UP above desired temp after the furnace shuts down. Forced hot air doesnt work this way so that why the setting is there. Instructions come with a new thermostat – Home Depot average cost 50.00

jay - February 11, 2014 at 4:19 pm

Ihave a boiler every time the pilot lights,the chimney pipe hums until the pilot goes out,is that caused by the draft or not

mike - February 10, 2014 at 2:42 pm

My 25 year old rheem furnace flame will come on but not long enough for the fan limit switch to be activated even at a low setting. The flame will stay on for about 30 to 45 seconds, how can i make it stay on longer to activate fan limit switch?

cyndi - February 9, 2014 at 3:33 pm

I have a 13 year old forced air gas furnace with a programmable thermostat. The thermostat says “filter” ( my son says its been displaying that for a while). I realized yesterday that the best wasn’t coming on. I checked it, cleaned the filter and manually activated the electronic ignition a couplrpe times but the burners didn’t catch. Then the ignition would light any more. Blower was working fine though.. Any ideas?

SAM - January 30, 2014 at 8:34 am

I have a gas hot air furnace with a programable thermostat.
Lately (about the last two weeks) the heater comes on for a couple of minutes, shuts off and then comes back on in about five minutes.
Also sometimes when the heater comes on I can hear a blower fan come on (which I think is a fan that clears out any gas that might be in the heater before the burner comes on) and it will run for a long time, (eight minutes one time until I turned the thermostat off) normally it only runs for about one to two minutes.When I turn the thermostat back on the heater works normally until the next time it acts up.
I have changed the batteries in the thermostat and replaced the filter in the furance.
Any ideas on both of the conditions ?
Thanks, Sam

Tim - February 4, 2014 at 8:42 am

Try taking your programable thermostat away from
its wall attachment and cleaning all the contacts
That go into the thermostat housing with alchohol.
Also clean the area where the thermostat senses the
Surrounding air temperature.

Plum - January 30, 2014 at 6:47 am

My furnace is at least twenty years old. It’s gas
I use a nest thermostat. ( which I love) my question is ; when the thermostat fist ignites ( when I run up the heat or request it turn on) it makes a
It makes a whining noise then my floor shakes and it feels like there was an explosion in the crawl space
Then the heat turns on and all is normal
This has been going in for a few years

Plum - January 30, 2014 at 6:44 am

It makes a whining noise and then the floor feels like there is an explosion underneath
Then all is well and the heat comes on

Michael - January 29, 2014 at 11:02 am

We live in a 10 yr. old, single story, slab foundation home with an open floor plan and relatively high ceilings in the main living space. Our furnace is running constantly and seems unable to get the house up to temp. The outside temps in Alabama have been much colder than normal lately and our furnace is running for 20+/- hours just to keep the house at 62 degrees. It is a gas furnace with an electric igniter. I’ve checked all the registers and they’re all open. We’ve replaced the filters on the returns (we have a finished room above the garage). We have a Nest Gen.1 thermostat. There are 4 appliances running off the gas supply (fireplace, furnace, water heater, stove/range). Ever since the stove was installed we’ve been experiencing gas flow issues (we think the main inlet pipe from outside at the meter is too small – the house wasn’t originally setup for gas stove/range). Could the lack of gas be affecting the furnace’s ability to heat correctly? The burners are all blue and appear to be burning at full strength. HVAC guys inspected ducts and furnace and said everything looks brand new. Any other ideas?

Salina - January 28, 2014 at 11:29 am

While the furnace is running, meaning the thermostat kicks on, the burner ignites, and then the blower kicks on, you can hear the burner igniting the more than once while the blower is running and before the normal cycle is complete. Is this normal?

Margaret OBrien - January 27, 2014 at 9:13 am

We didn’t change our filter and now the heater doesn’t work. Would this cause the heater not to work? What is the best plan for our situation? Please, we are
cold in Lancaster!

Sherry - January 27, 2014 at 12:25 pm

Yes. If you change your filter it should work again. I have completely removed the filter for a temporary solution.

john poczynek - January 19, 2014 at 11:53 am

where can i get a gas furnace guide

john poczynek - January 19, 2014 at 12:00 pm

I have another question.I believe blower axil is steel rotating in brass or bronze sleeve bearing.what kind of oil do i use to remove squealing.

william - January 17, 2014 at 5:40 am

Very helpful information. I’m impressed.
What would be the problem if the furnace motor wont stop running . The temperature inside the house is 80, even though it was set on the thermostat to 71

Frank - January 26, 2014 at 7:02 am

I had the same problem a few weeks ago, the thermostat was faulty and after it was replaced the problem was cured,hope this helps tyou.

Uttam - January 6, 2014 at 6:11 pm

My gas furnace does not function properly, at least three-four times or even more a day I have to turn on-off the switch to work. The Thermostat will rise up to 60-70 degree F than after that falls below 50-60 degree F and stops. Again have to repeat the same procedure, play with the on-off switch. Any suggestions please?

Sam - January 17, 2014 at 5:35 pm

I have the same problem. I am going to call someone in to help in the next day or two. If I find a reason I will let you know.

Scott - February 6, 2014 at 4:06 pm

Did you ever receive an answer for this problem?

Dee - February 7, 2014 at 10:52 am

Uttam, Make sure your Thermostat is set on “MANUAL” NOT Program.

Troy shire - February 16, 2014 at 5:08 pm

Is the furnace locking out? Any codes flashing on the control board?

Angela - January 4, 2014 at 9:49 pm

Hi I live in a condo building. They recently did repairs and replaced parts on the building’s furnace system. Now every time the heat kicks on and blows hot it gives off a smokey burning smell. I know sometimes new parts can give off a smell as the oils burn off but should it be lasting for over a week or two? Also are these fumes dangerous or toxic. People I’ve talked to say no but I’m concerned.

Thank you!

Ralph - March 23, 2014 at 2:15 pm

As a safety precaution, you could install a carbon monoxide detector. If the heat exchanger is damaged (in the furnace), you could be smelling the oil being burned, which is toxic.

Phyllis - January 4, 2014 at 8:59 pm

I just had a A/C person put a new non programmable thermostat in and every since he installed it, the heating system will stay on for only 5 minutes and goes off. Then 15 minutes later it will come back on again and stays on for 5 minutes again. I am afraid my electric bill is going to be extremely high. Please advise what should I do.

Jerry L - January 3, 2014 at 8:45 am

I just had my furnace replaced two months ago, and it seems as though it runs almost constantly. It only shuts off for a minute or two, then it kicks on again. Could this be a thermostat problem since it is the original and 15 yrs old, or does my new furnace need some adjustment?

Rita - January 16, 2014 at 8:47 am

Hi Jerry. the latest thing that no one is aware of is that hackers are taking surveillance on other people’s home and tagging onto their furnace. i am having this problem right now and no one believes me. pay special attention to sounds that you hear around your house. make sure that they’ve always been there. its not just cyber crime anymore. please dont write to this email because i will not get the message. i dont log on anymore.

Steve - January 22, 2014 at 7:47 am

ROFL x1000

Matt - April 2, 2014 at 8:10 pm

There is a good chance it’s the thermostat. Try cleaning the contacts on the thermostat. If that doesn’t work get a new thermostat.

Joe - January 1, 2014 at 8:44 pm

I have been older furnace probably about 15 years old. I have been living in this home for one year now. The symptoms I’m experiencing is that if I set my thermostat to 70° or more that the furnace will heat but stop short. At which time the furnace needs to be power cycled for about five minutes to function again. Any thermostat setting below 70° the furnace runs like a champ. So basically my house is always about 68° Max, even though I would like it warmer sometimes.

ARACELY - January 1, 2014 at 8:30 pm


clarence mead - December 31, 2013 at 8:53 am

have a furnace that want to keep jumping fire to the inside of the burner .some times the pilot light will go out when it shuts done

Bill - December 29, 2013 at 6:05 am

Thermostat reaches 4 degrees above set temperature and burners shoot down. Blower motor keeps running and blows cold air. Have to shut blower motor off manually. An hour later I can turn switch back on and burners and blower motor start when Thermostat set temperature is reached. Shut down is the same problem, blower motor won’t shut down.

Tino - November 13, 2014 at 1:21 am

More likely the high limit switch is failing and goes erratic, it controls when the fan turn on and off. bimetalic switch gets tired.

Sarah - December 27, 2013 at 5:44 pm

my gas heat comes on but doesnt kick off i have to turn it off on the switch so sometimes i wake up cold bc we have to get up and down to turn it off and on and sometimes its so hot u cant stand it anyone know what it could be…. we already changed thermostats didnt help

brian - December 23, 2013 at 5:34 pm

My ruud gas furnace was working fine. And all of a sudden it made a loud popping sound. Turned it off and cut it back on and ran it. It worked just makes a loud racket when running. What can the problem be?

Don - January 5, 2014 at 10:58 am

Your fan is coming apart!!!

lorine - December 16, 2013 at 10:20 am

why is my furance keep going out the landlord said it was the filter he change the filter and it happen again i know it is not a comment but it something i need to know

Sherry - January 27, 2014 at 12:22 pm

Did you ever find a solution? I have the same problem and the only thing that worked was to remove the filter? I know this is just a temporary solution, but I was cold!

Joe Scelsi - December 11, 2013 at 6:01 am

I have a Rheem gas furnace. The burns will ignite and stay on, but for only a few seconds and then turn off. If I cycle the thermostat a time or two it will come on and remain on until desired temp is reached. I replaced the flame sensor, but that had no affect. What do you suggest to try next?

Wayne - December 9, 2013 at 9:05 pm

Blower motor cycles on and off for a second or two a few times while burners are on. After going thru heating cycle, burners turn off, blower goes on as normal but when it is time for the blower to turn off, it cycles on and off quickly for multiple times before turning off. Any ideas??? Thank you.

Tino - November 13, 2014 at 1:26 am

More likely the high limit switch is failing and goes erratic sometimes and not when tech checks it, it controls when the fan turn on and off. bimetalic switch gets tired and fails

Chris - December 8, 2013 at 4:05 am

I have a gas furnace and it started making weird noises. I turned it off. I turned it back on …. 3/4 hours later and it made a HUGE ROAR like an airplane sound and upstairs in our master bedroom I could smell smoke. The smoke smell is only in that one room … 3 levels up from the furnace. The heat is on now and the house is heating properly …. your thoughts please?

George - December 7, 2013 at 9:53 pm

I have a really old Carrier furnance, maybe 25-30 years old. About two weeks ago we started noticing a loud noise(sounds like an airplane flying through) from the furnace when it’s coming on, maybe when it shuts off too. Furnance is located in the basement, practically shakes the floor when it’s clicking on?? Any suggestions? Thanks, george

matt - December 7, 2013 at 9:32 pm


GENE - December 4, 2013 at 2:23 pm

I own two reznor heaters model 105 CEEXL for my garage. One heater works perfectly fine, but on the other one when it first starts off the motor turns on and off while the burner is operating. I took all the parts from the good heater and put them into the one not and the same thing happened. When the bad heater is on for about a period it runs normal. What is my problem?

brad - November 25, 2013 at 9:44 pm

I have an arcoaire 80% furnace, approximately 13 years old. I can turn on the fan at the thermostat, and it runs fine. When I turn it to heat, the small fan runs that is connected at the top, I’m guessing to force the fumes out of the heat exchanger? I can see the ignitor get red hot inside and stays lit for a few minutes, then shuts off. But the small fan continues to run. I’ve verified that the gas valve is on. And I have gas going to my hot water heater. Any suggestions?

jamie - November 25, 2013 at 8:50 pm

The furnace blower is constantly going on and off every minute or so. The burners are always lit up to. I thought they are only lit when the blower turns on? I was told it was the regulator….but it sounds like the blower and pilot? I don’t understand why they always stay lit

Sue - November 25, 2013 at 1:59 pm

My furnance makes a loud whinning sound. It starts before the burners ignite and continues throughout the complete cycle. The furnance heats fine. I made a videoing of it. The burners ignight at 7-8 seconds in the video and the blower comes on about at 43.
A handyman helped me by cleaning it out and the sound started afterwards. I had it professionally cleaned less than a year ago.

don - November 24, 2013 at 6:02 pm

Pilot will light & stay on burners come on furnace runs untill thermostat shuts it off .the pilot goes out. Is this a thermocouple problem?

Brad - December 30, 2013 at 6:27 pm

I have the same issue, Any solutions?

Dana Gehring - November 24, 2013 at 4:28 pm

My furnace runs all the time… it continues to call for heat. I have replaced the gas valve, fan relay switch, thermostat (inside furnace box), and just bought a new thermostat to mount on the wall and hooked that up but it continues to run constantly. It’s like the thermostat isn’t there. We tested the wiring running to the thermostat by unhooking both wires from furnace…furnace fan runs even with wires on hooked. It doesn’t call for heat though. What could it be? I have called furnace man to look at it but he can’t figure it out. One thing if I switch it off on the breaker I can hot wires?

jt - December 6, 2013 at 6:41 pm

Just a thought. If it has a control board then it could be that. Maybe there is a set of contactors that are stuck somewhere. Maybe its the fan center.

R. Reed - November 24, 2013 at 1:01 pm

We have a gas furnace, and it won’t come on until you flip the breaker switch, then it comes on for less or at least 5 minutes, shuts off and doesn’t come back on again. Then out of the blue it comes on itself. What’s up with that? We replaced the relay board, and thermostat. It still isn’t right, and put new batteries in the digital thermostat. Can’t figure it out. HELP, can’t afford a new unit.

hollie - December 3, 2013 at 10:24 pm

ours is doing the same thing.. did you find a fix?

April - November 24, 2013 at 7:33 am

hello. Ive noticed between last year&soo far this cold weather soo far it seems like the colder it gets outside the less my heater kicks on by itself if I play with the switch on the tjermostat(an old one non digital) it will kick on..now when its above 45 degrees outside or we get a warmer day the heater will kick on regurarly but the colder it gets it will kick on less&less ..last nite where I liv e was very cold my jeater did not kick on at all I lay in bed listening out&waiting for the heater but nothing until I went down &messed with the thermostat which by that time the temp in the house was down to 40° never been that low &after that one time last nite it did kick on it did not kick on no more during the nite…what can be the issue??

Denises - December 7, 2013 at 5:33 am

April, I have the same promblem. Did you resolve yet? If so, what caused it?

Debi - January 3, 2014 at 10:38 am

I am going thru this right now. still nothing.. I keep messing with the thermostat and sometimes it works sometimes not, I have mine set at 82 and the room temp is 66. And you are right the colder outside the worse inside, why would that even matter right? my furnace is fine, I have my friend look at it and all is good and clean , and it will heat but not when its suppose to. so aggravating.

Evelin - November 23, 2013 at 9:19 pm

Our gas furnace has been turning off without it reaching the ‘designated temperature’. Even when we set the heat to be 75 but the temperature in the house is 70, the heater will turn off. It turns off more frequently than it needs to be. We’ve replaced the thermostat but the problems continues. What could it be?

Lee keita - November 14, 2013 at 7:20 pm

Lately my furnace stopped working. When I turned the circuit breaker off and then on, the furnace starts running for few minutes and the circuit breaker goes off again. When causes the furnace circuit breaker of the main switch panel to go off when the furnace starts running? Is that an electrical problem or a problem with the furnace?

bkanvick - November 28, 2013 at 6:16 pm

I would suggest that you have a blower motor that is drawing to much current and that is what is causing the circuit breaker in the panel to trip. Too much current draw.
You could also have a circuit breaker that is old and it needs to be replaced.
Hope this helps.

An electrician might be the best one to call to measure the current draw and determine if it is the blower motor or the circuit breaker. If the motor is wearing out then the electrician should be able to replace the blower motor.

lynn - November 13, 2013 at 9:44 am

Hello, so i have a question while waiting for someone to come fix . My gas furnace seems to work perfect and i get good heat… But since i moved in here my furnance wouldnt kick in unless the thurmoastat was turned up to 22+ and then it gets so warm that i keep turning it up and down and up and down… But yesterday i turned it up for it to turn on and it never kicked in… So i went down and flicked the switch (which is like a light switch on my wall near the furnace which turns the power to the furnace on and off) from on to off and then back on and it kicked in and itll work fine untill the house is hot enough and it kicks back out but then i have to turn the switch back off and on again for it to kick in again… What can this be?

Dennis - November 9, 2013 at 7:03 pm

My furnace which is rather old is giving me fits again.Back in the spring a guy came out and replaced a part.But now its doing about the same thing.It comes on and heats for a while then the heat goes of but the continues to run,I finally had to shut it off at the circuit.Anybody out there got any ideas,your thoughts are appreciated.

DWood - December 1, 2013 at 10:13 am


I had the same problem with my older furnace and it turned out to be the filters. I was using the new style allergen blocking kind. These do not allow enough airflow for the older furnaces so a thermo switch trips. Replace with the cheap filters that look like they might block a bird from getting in and it just might help you out. Good luck.

Tino - November 13, 2014 at 1:33 am

More likely the high limit switch is failing and goes erratic, it controls when the fan turn on and off. switch gets tired with old age.

Pat - November 9, 2013 at 1:27 pm

I have had my furnace looked at twice within a two week period by a professional & the furnace won’t stay lit,, sounds like I’ve paid him for nothing, would the cause be the chimney causing the pilot to go out, I think there is a draft coming in from it, but I don’t know,, that’s what the HVAC guy mentioned

jack - November 7, 2013 at 4:48 pm

did not see an answer to my concern. when we go to turn furnace on just get buzzing noise from furnace?

Mary - November 3, 2013 at 5:15 pm

I have a model #58ZAV1151 4116 Carrier furnace.It worked great for the three yrs I have owned this home.I had to have the blower motor replaced in July.When I turned the furnace on recently it wouldn’t come on and cycle correctly.It was working properly on one stat now it clicks and ask for heat and nothing Three HVAC co’s have been here in the last 10 days one of them Carrier certified and they can’t find the problem.It is now not comming on at all unless I turn it off and back on it cycles just like it is suppose to but won’t on its own.
Oh and I have three zones in my home and three stats

Jim Dinsmore - November 2, 2013 at 9:11 am

Sorry, the ignitor is at the bottom, not the top.

Jim Dinsmore - November 2, 2013 at 3:15 am

I have replaced the ignitor on my Ruud system & it still will not glow/light the furnace. I have looked inside the system and simply cannot find the flame sensor to check out. My system has 4 vertical burners, with the ignitor at the top. I know what a sensor looks like, but it is nowhere to be found on the inside of the furnace.


John - November 24, 2013 at 8:36 pm

It may be in the area near the heat exchanger and should the flame sensor should be in front of one of the burners. Hope this helps

clay - December 9, 2013 at 10:58 am

It should only have one wire running to it and be mounted on the front side of the burner assembly near the burner farthest from the ignitor.

Jim Dinsmore - November 1, 2013 at 9:59 am

I have a Ruud air/heating system with a Norton 201N furnace hot surface ignitor. The ignitor would not ignite so I replaced it with an OEM upgraded replacement (201-904). It still will not glow and ignite the gas. Thermostat is ok.

Thanks. Jim

Theresa - October 29, 2013 at 3:14 pm

I have a Rheem gas furnace. My furnace works. It ignites with no problem. The only thing that is bothering me is that there is a loud hissing sound that is constant. It’s been hissing for hours today. It sounds like the noise you would hear if your toilet was continually running or if you heard your neighbor’s shower running… but it’s in the furnace area…not the actual furnace…I thought maybe it was the attached humidifier but I turned that off and it’s still hissing. I wish I could upload a video so you could hear the sound. It’s the sound that happens before the heat comes on but even with the heat turned off…it’s still hissing. I don’t get it.

Kyle H - October 27, 2013 at 9:19 am

Hello, I own a mobile home and just tried to turn on the furnace since it is getting cold here in Michigan. The furnace powers on, I checked the switches and gas valve, and they are all on. I can see the ignitor thru a small circular window, and I have watched it until it created a flame. Around a minute or so later, the upper fan kicks on, which makes me believe the furnace is acknowledging that it is up to the proper temperature. However, only cold air blows out of my ducts. I can not figure out why I am getting such a strong flow of air, but no heat. Any suggestions would be greatly appreciated! The furnace is a Coleman Evcon unit.

John - November 24, 2013 at 8:32 pm

Do you have enough gas in your tanks? What is the pressure in your gas valve?

Stephen - December 24, 2014 at 4:17 am

The flame sensor at the pilot needs cleaned. As it soots up it doesnt sense the pilot flame and prevent the gas valve from allowing the burner to engage.

Cara - October 25, 2013 at 10:28 am

when we first turned on our heater (one cold weekend) we got a horrible smell. To me it smelt like fertilizer? or something died ? Also sometimes like a burning smell. My landlord came over, but doesn’t think anything is wrong. The house temp is set at 69 yet in the morning its around 65. reading your trouble shooting, I think it might be the fan is not working. It doesn’t seem like some of the rooms are getting heat i.e. my room. I just can’t figure out the smell. Any suggestions ?

Jennifer - November 22, 2013 at 11:49 pm

Cara, I’m not an expert, just a lay person, but I know that when the furnace is turned on for the first time after not being used for a while, you’ll smell the dust burning off etc. – it will smell as you described. As long as it goes away after a little while, I wouldn’t worry about it. I get this every time I turn on my furnace if it hasn’t been turned on for a while. If the smell happens every time the furnace comes on — even if it was just on an hour before, for example, that’s something different. Regarding the house temp being lower than the set temp, on my thermostat, at least, there are two arm-like things, where you set one higher than the other. The furnace will turn off at the high temp, then turn on at the lower temp. So if the lower arm is set at 65, there will be times when the house temp is 65. Put these close together and you’ll have a more constant temp. Also, if some of the rooms are getting heat and some aren’t, it doesn’t sound like it’s the furnace. You should double-check that all the vents are open. As I said, I’m a lay person, so I don’t know that this will help you at all, but just maybe it will… :0)

Stacie Castillo - October 23, 2013 at 6:26 pm

At first I couldn’t get the pilot to stay lit. Now, it will light. I turn the knob to the “on” position and set the thermostat. The fan will kick on and I hv fire for a little while, then my flame completely dies (pilot & all) . This leaves gas running. Any suggestions?

j. s. - October 27, 2013 at 11:30 pm

I had the same problem and my gas flow just wasn’t turned up high enough to keep it lit. Drafts would blow it out. I’d check that

Ralph Bledsoe - November 24, 2013 at 9:11 am

I turn my furnace on the igniter come on then a click flame on about 15second it blows out. The igniter go out

Marshall - October 23, 2013 at 12:16 pm

I have an older furnace [Goodman] with a pilot light that will kick the burners on when set to the Auto position. Instead of the fan kicking on it heats up then kicks off when the temp gets to high, the fan never comes on. It will kick on when the heat is turned up and I set the fan to ON [both the fan and burners]. The furnace burners will shut off when the temp is reach but not the blower which is set to on will continue to run. I just replaced the main valve. Any suggestions. Could this be the thermostat?

murray - November 11, 2013 at 8:53 pm

the problem is probably your fan limiter switch. when your furnace reaches proper temp the burners kick off first and your fan should kick off about 2 to 3 min later, the limiter switch tells it to.

Larry - October 18, 2013 at 6:36 pm

I have a old Rheem central gas fired heater. It has a pilot light. The unit will light the main burner, set for about 1 minute and the blower fan will come on and run about 1 minute and then the blower will shut off. the main burner remains on and in about 1 minute the blower fan will come on and again run for about one minute and shut off. this cycle will repeat. the blower fan motor was replaced about three months ago. could this blower motor be running at to high of a speed and causing this or if not what might cause this situation? unit is around 35 years old.
Please advise. Thanks

Tino - November 13, 2014 at 1:37 am

High limit is failing

John - October 18, 2013 at 4:02 pm

I just replaced the igniter on my heater. It comes on for a few minutes and the gas shuts off. The light below blinks 4 times and the door states its the limit fuse. Fuse on board looks fine. Don’t know why it runs and heats but only for a few minutes.

ELEANOR - October 15, 2013 at 9:59 am

Last winter had trouble with furnace turning on, I manually flipped the switch a couple of times, and it would come on. Now, nothing, no heat. Any suggestions??

patti kauffman - October 23, 2013 at 11:17 am

Call a technician. Do not let anyone other than HVAC work on your unit. My roomate wanted to check the unit but he has limited experience with repairing gas heaters. Although he was a homeowner, the gas units are way too specific to be toddled with by a nonprofessional. He fixes his own car but that is a different animal. I am one to try to save money I dont have but after using the space heaters last year, I finally saved the money. I found a company and it was the ignitor. Two other companies were talking about buying a new furnance because its 25 yo. Buyer beware.

kent kirkland - October 11, 2013 at 1:01 pm

my gas furnace is not working properly. i pull the wire harness off and blower comes on,i put harness back on and it shuts off after between 1 to 2 minutes. also i see no flame through view hole .

Roger - October 11, 2013 at 6:13 am

My furnace seems to work but the blowing runs almost continuously! Does anyone know what I can do to fix it?

Jim Benson - October 16, 2013 at 10:55 pm

It depends on the age of the furnace. I have an 85 and keep it clean, oiled and safety parts bench tested every yr. New ones have an electronic solid state board that keep the blower part running based on time where mine is based on temperature. The board may be bad or your on manual/cool and some stats have a fan only option. If the heat goes off but the blower stays on more than a few minutes to clear heat/gases out then contact a HVAC technician. It may be required under new BOCA/NFPA codes. Hope this helps.

Tino - November 13, 2014 at 1:38 am

Bad limit switch drives furnace nuts.

Ronald Tratt - October 9, 2013 at 6:15 pm

I have a year old Airtemp furnace, model VG7s090d-35c.Problem is cooling blower runs radomly when not calling for heat. Can you help me with this problem? Thankyou

Tasha - September 24, 2013 at 8:23 pm

Does anyone know how to completely turn it off? We don’t want it on this winter and are trying alternate ways to heat the house. We turned all the thermostats as low as try will go, but we can still hear the heater turn on

Jim Benson - October 16, 2013 at 10:57 pm

Turn off the units power switch. If not equipped shut off the circuit breaker. Still a problem ? Get a sweater because you have a ghost that likes it warm!

j. s. - October 27, 2013 at 11:33 pm

After you’ve switched it off turn off your gas flow and your safety valve and unplug it. It should stop running.

paul A - September 22, 2013 at 9:42 am

i turn my furnace on and i hear a buzzing noice from the relay the motor on the bottom of the exhaust pipe is hot to the touch. when i turn the blower motor to the summer setting it blows good but it wont kick in on the auto setting what should i do

Nick Favuzza - September 20, 2013 at 9:23 am


I have 3 floors and the heat works fine and is coming out fine on the top floor

and the basement is fine there is a thermostat on each floor the main floor

no heat coming out of the vents cheched the thermosat put in new batteries

what can the problem be? please help

thank you.

Jim Benson - October 16, 2013 at 11:01 pm

You have multiple zones? Then that sounds like baseboard hot water with zone valves, or dampers controlled by stats? Check stat programming, it may be that or check that heat is switched on, after stats are ok, zone valves and/or dampers may be bad.

Maggie - August 14, 2013 at 3:29 am

My thermostat for my gas furnace suddenly changes to a temporary setting without being touched. The thermostat has been changed three times. The repair service feels someone is changing it which is not true. They don’t check anything else even when I tell them it suddenly happens when I’m the only one in the house. What could the problem be

Jim Benson - October 16, 2013 at 11:02 pm


Bob - July 5, 2013 at 1:46 pm

My furnace has been randomly shutting off. It’s a York System and only about 5 years old. Repairman came out but by the time he got there it already started working again. He said he needs to see it while it’s broken to diagnose. When it turns off I normally take out the filter and put it back in a few times and it turns back on. This has worked at least 5 times. Repairman said it’s a coincidence but I don’t see how that’s possible. Could there be an issue with the filter that is causing it to shut off? It looks clean and I relpaced it only a few months ago.

Jim Benson - October 16, 2013 at 11:04 pm

Could have something to do with your doorswitch. When its off micro switches open circuit. So when he gets there its on again. Next time let it off and dont open or touch it so he can diagnose the problem.

Becky - June 18, 2013 at 2:14 pm

My new furnace…10 months old has started to leak water when the air conditioner is in use. The guy who put the furnace and the central air unit in says that the furnace got too hot because I didn’t change my filters. I have changed the filters monthly and I don’t believe that caused the issue. He says that he will have to open up the furnace and replace an expensive part which will take a lot of time. I have water all over the floor.I have a hard time believing that the filter caused the problem…and is it my fault? And how do I redeem this issue. This is an expensive Amana unit!

robert trudeau - February 4, 2015 at 11:44 am

you have a clogged condensate drain for the air conditioning coil on top of the furnace.minor fix

donna clark - June 18, 2013 at 12:45 pm

I have a gas furnace in the attic. I turn the thermostat to cool 76(below the house temp) and nothing happens. It clicks a tad as if it wants to come on but nothing. I had someone look at it and they said the control board is bad. Now, how do I know it’s the whole board and not just a new fuse on the board. Also, is that something we can install ourselves? Thanks, Donna

Jim Benson - October 16, 2013 at 11:07 pm

Component level semi conductors make up “boards” and no, I advise you dont touch the board but if u feel better get a second opinion.

greg andrews - June 17, 2013 at 2:14 pm

furnace dosent light properly from front by the standing pilot, to the rear any more. it lights with a bang and blows out the pilot. it has done this before but i cant member what fixed it. altitude is 7000 feet. runs on propane, size of pilot is good.

jerry - May 26, 2013 at 6:47 am

My furnace puts out a very bad smell in the basement but it doesn’t seem to come up through the registers.

donna - August 11, 2013 at 9:23 am

I was getting a nasty smell from my basement into my hallway at the top of my basement steps. It would return every spring. I used to think it was a dead animal in my walls, but ruled that out when it came back every spring. Finally decided it had something to do with natural gas, and finally had a furnace guy come in this week. Turned out, the vent pipe in my chimney isn’t big enough to give me a good updraft, so the burned natural gas was not sufficiently venting up and out of the chimney. It was hanging around in my basement and wafting up into my house. Very dangerous ,healthwise, to humans and pets. They put in a system that deletes my chimney all together, because my old chimney didn’t have room to put in a bigger vent pipe. The new system is vented out through a basement window pipe,,set up to draw it out by a complex, computerized fan that comes on when my furnace or hot water tank is working. It was not an issue in winter, because when it’s cold out, my furnace works more, heating the chimney and pulls the draft up and out. In warm weather, only my hot water heater was working . so it didn’t heat up the chimney enough for a good upward draft. Cost about $1500.00.

Ralph Cooper - May 22, 2013 at 7:08 am

I have a Honeywell furnace.. the circuit board recently died, and i bought a new one and replaced it.. I also took out the air filter, which was dirty.. that was located near my thermostat.
After i replaced the circuit board (model st9141 A1002 part # 406650) it worked for 1 day.
Then today, i come home and i have 4 flashing green lights saying its a “no airflow circulation” code.
The furnace motor-fan still works, but the actual HVAC central air unit fan didnt come on..
Is it because i need to put in a new air filter.. or is this because of something else?

Lynn Hyder - May 13, 2013 at 7:14 pm

I have a question and I hope that you can help me. I change my furnace filter every month. The last 2 months the filter has no dirt or dust in it. Usually it needs changed every month. What should I do? Thanks Lynn

Karie Fay - May 18, 2013 at 11:44 pm

Hi Lynn,

Kudos to you for changing your filter so regularly. Many people tend to skip it or stretch their change time, which can cause so many problems – from high electric bills to actual damage. Still, I must confess surprise that you ask why it doesn’t seem dirty enough?! Honestly, I think that’s a good thing!

I worked in the air conditioner filter business for some time – with “washable” electrostatic filters – and I am curious what type of filter you are using? Depending on the type, you may not see some of what’s actually trapped in the filter media. Contaminants can be microns in size – smaller than a human hair’s thickness – so there may be more than you realize.

Why would there be less than usual? Most likely something you’re not accounting for. Has your home been closed up more than normal? Has the road outside been paved? Have you suddenly started dusting your home more? Your furnace, typically, pulls air from your house to circulate through the system. Anything that lowers the dirt and dust in your home will therefore mean less in your filters.

To save money, try switching to an every-other-month filter change schedule. Or, switch to a washable filter and simply rinse it out every 4 to 6 months instead. But don’t worry about your clean filters! Feel lucky! At least, that’s my opinion.

Hope that helps,
Karie Fay

Tim Ryder - May 11, 2013 at 6:33 pm

My furnace’s blower isn’t working. The squirrel cage can spin freely by hand, the furnace ignites and the limit switch kicks on the blower motor (at least I can hear the motor get louder) but I just don’t get any air moving. As a result the flames are still on and it smells like burning but again no air. I checked the Limit switch mounted in the main air duct and it has 0 ohms resistance when its cool. No conductivity.

Any ideas why my blower doesn’t spin but it sounds like it tries to start up after the burners are lit for a minute or so.

occasionally I also get the 4 flashes on my status light for the board.

Kevin - May 17, 2013 at 2:39 pm

Either the startup capacitor is shot or the motor itself. Most likely the motor.

Mike - October 14, 2013 at 8:40 pm

0 ohms means 100% conductivity…. if it flashes or stays on 1… then no continuity.

Change the motor.

Lillie Wisooker - April 25, 2013 at 6:13 am

Our furnace sounds like an airplane is landing whenever it running and the main pipe coming out of it is scorching hot to the touch. Is that normal?

Karie Fay - May 4, 2013 at 5:05 pm

Hi Lillie,

Great questions! I understand your concern about the flue pipe temperature. You didn’t mention what it’s made out of, so I assume it’s the typical metal? Newer furnaces vent very little heat – they are high-efficiency and basically wring every drop of usable heat from the combustion before venting it from the home. As a result, they often use PVC vent pipes. Older furnaces allow more heat to escape. This is a good thing, as it carries emission gasses from your home (heat rises). In fact, a too-cool vent signals a problem as well!

Anyway, the heat inside the vent near the furnace is likely around 400 to 600 degrees. So yes, I would expect the vent pipe exterior to be blistering hot!

As for your second question, really loud sounds like you are reporting make me think either a bearing going out (on the blower) or a problem with the furnace blower. Does it only make that noise when the heat kicks on? If it’s all the time – even when the furnace is idle or before it begins blowing – I would be concerned that it’s the burner. If so, it could be a dangerous problem if it’s causing any overheating or is somehow connected to the flue temperature. I would urge you to have a professional look at the burner if you are unable to determine the cause.

I hope that helps,
Karie Fay

Todd - April 20, 2013 at 5:03 pm

also I hit the reset button…the tubes just wont kick on and ignite. but everything else checks out ad is kicked on

Todd - April 20, 2013 at 5:02 pm

My thermostat works, pilot works, fuse breaker ok, heater motor on and ok – yet the furnace doesnt ignite down the tubes. What can it be?

Karie Fay - May 4, 2013 at 1:58 pm

Hi Todd,

Sorry to hear you are having problems with your furnace. It would help tremendously if I had more details. I assume you have a gas furnace and the blower is okay, your electricity is ok, the thermostat checks out and the pilot light is on, right? By tubes, do you refer to the burner? That is, the pilot lights, but the burner won’t come on?

If that is the case, I think you would find my article on Gas Fireplace Troubleshooting helpful. A gas burner system is much the same whether furnace or fireplace, after all.

Here’s a few snippets I find relevant to your situation:

Thermocoupler and Thermopile:
Once the pilot is light, it heats up a thermocoupler and a thermopile. The thermocoupler, sometimes referred to as a heat or flame sensor, is made from two different metals that create a small electrical charge when heated by the pilot. This electrical current causes a magnet in the gas valve to shift open, allowing gas flow. If the pilot isn’t lit, the magnet shifts again, causing the gas valve to close. In essence, the thermocoupler is a safety mechanism. Likewise, the thermopile is a system of thermocouplers that create a greater electrical current, moving a larger magnet that allows gas to flow through the main gas line into the burners.

Knowing this, if I am interpreting your problem correctly, I would start by checking these things out:

A dirty pilot light orifice – the area from which the flame emerges – or dirty burner jets may cause problems with the burner operation. Cleaning and removing soot with a little steel wool is the solution here.

One of the most common causes of burner failure is due to loose or faulty wiring. Visually inspect the wiring, looking for unattached or obviously damaged wires running from the pilot light assembly. Consult a professional for wiring assistance.

As mentioned, the ignition system relies on generating an electrical current to open and close the gas valve, allowing fuel to flow to both the pilot and the burner. Other electrical circuits run to the appliance switch and thermostat. Low voltage to any of these parts can lead to a poorly functioning or inoperable burner. A service technician can quickly and easily test the circuitry with a multimeter and diagnose the exact problem.

Another problem that can cause burner issues is a malfunctioning thermocoupler. As with a thermopile, thermocouplers may wear out and need replacement after a few years, or may simply not fit tightly inside the valve. A professional can easily test and replace as needed. Or, clean it with steel wool.

Hope this helps!
Karie Fay

Dot Morris - March 18, 2013 at 11:27 pm

add furnace work fine until tonight.

Dot Morris - March 18, 2013 at 11:14 pm

I came home from work apartment was 91 degrees tstat sat on 70. had to turn off gas to get furnace to turn off. Even turning off tstat and electric switch did not turn furnace off. Any idea what hap;pened to keep it running?????

Karie Fay - May 4, 2013 at 1:17 pm

Hi Dot,

Sorry to hear about your problem. Have you been able to fix it yet? If not, hopefully I can give you some ideas.

You say the electric switch won’t turn it off. Did you try the breaker too? If so, then I think we can safely assume the problem isn’t in the thermostat itself.

I am not sure what brand furnace you have or other little details that might help me. Still, off the top of my head, I am thinking the gas valve may be malfunctioning. If it is stuck open, it will keep heating because it literally can’t shut off.

You might try “percussive diagnostics” – tap on your furnace. Hard. Sometimes, something called a “limit switch” goes bad. The limit switch tells the furnace when to turn on and when to turn off again. If it sticks on, the furnace stays on, of course. Not only is your home getting too hot, so is your furnace.

Some people bang on the furnace to tell if this is the problem. If you know where the limit switch is, bang directly over it. If it works and the furnace turns off, you will need to replace the limit switch. It’s not horribly expensive or difficult.

I hope this helps!
Karie Fay

ELEANOR - October 15, 2013 at 10:12 am

you are talking about a switch, maybe you can help me. Last winter I had to flip the switch for the furnace to come on. Not all the time, but enough. Now it wont go on at all, any suggestions??

Mark - Gas Furnace Guide - December 20, 2012 at 3:55 pm

A well written and thorough guide to furnace troubleshooting, from a homeowners perspective, good job! You mentioned filter changes, and one thing to be noted is that its the easiest thing for a homeowner to do, that will prevent 90% of furnace problems! We recommend 30 day filter changes whether they’re needed or not.

Good article!