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Furnace troubleshooting questions with answers index

Below we have quick links to pages where problems and solutions are discussed for your quick reference and hopefully a quick solution to your problem. Special thanks are in order for the many people who took the time to make the YouTube videos that are included on our pages! I know that it is much easier for me to learn if I can see the problem and repair through a video or picture! Near the bottom of each page there is an area that allows you to comment or ask questions. If you have any questions please send us an email anytime: or comment on the perspective page. We would love to help you out, answer your questions and earn your business! Hope you have a blessed day! Steve & Barbara Arnold

One of my favorite quotes by David Jeremiah: “Nothing is more valuable than helping another person succeed!”

  1. Problem: Furnace blink code shows I have a pressure switch problem. Replaced pressure switch. Still have a problem?
  2. Problem: Will the pressure switch correct my water drainage problem? (With two YouTube Videos)
  3. Problem: Why does my furnace rollout switch have to be reset so often? Why do rollouts have different temperature differences? (With two YouTube Videos)
  4. Problem: Why does my furnace air conditioner have poor air flow? (With one YouTube Video)
  5. Problem: How do I test and troubleshoot my gas furnace pressure switch? (With one YouTube Video)
  6. Problem: What is the sequence of operation of my 80% gas furnace? (With one YouTube Video)
  7. Problem: Furnace will not ignite. Ignitor will not glow. (With two YouTube Videos)
  8. Problem: Furnace or water heater pilot will not stay lit. (With one YouTube Video)
  9. Gas & Electric Furnace Troubleshooting Simplified (With one YouTube Video)
  10. Furnace Troubleshooting Flow Chart.
  11. Problem: Furnace comes on, doesn’t run long then shuts off. Will work if thermostat is turned way up. (With one YouTube Video)
  12. Furnace Hot Surface Ignitor Troubleshooting Videos.
  13. Problem: How do I wire up my new thermostat? What do the wire colors mean? (With two YouTube Videos)
  14. Thermostat Replacement (Video)
  15. Furnace Control Board (Video)
  16. Furnace Blower Replacement (Video)
  17. Problem: Burners ignite the gas valve cuts off after only a second because the pressure switch is opening for a split second.
  18. Problem: Furnace main burner ignites, the main burner stays on for 8 to 10 seconds, then shuts right back off (With one YouTube Video)
  19. Problem: I purchased a flame sensor from you for my Goodman furnace. The new flame sensor did not fix the problem? (With two YouTube Videos)
  20. Problem: Blower shuts off too soon, cycles off and comes back on within 30 seconds
  21. Problem: The fan on your furnace runs all the time and will not shut off (With one YouTube Video)
  22. Problem: Fan will not come on in the “ON” position or your fan will not come on when you turn the thermostat down
  23. Problem: Furnace, air conditioner heat pump will not come on. Blown fuse on board. (With one YouTube Video)
  24. Problem: Draft inducer will not start, ignitor will not glow or gas valve will not open.
  25. Problem: Electric heat will not come on, fan will not come on.
  26. Problem: Why do I have to replace my furnace ignitor every two weeks?
  27. Problem: My Trane IGN00145 Ignitor is going out too often? What could be the problem?
  28. Problem: I have a bad igniter is there anyway to light a gas furnace manually?
  29. Problem: Burners ignite the gas valve cuts off after only a second because the pressure switch is opening for a split second.
  30. Problem: No gas.. bad control board? Frazier Johnson heater.
  31. Problem: My furnace is making a howling noise only in the winter time?
  32. Problem: Why is my heating bill so high? Over $500!
  33. Problem: Could a weak thermostat battery destroy my home?
  34. Problem: Furnace blower motor works intermittently?
  35. Problem: The heater comes on, the gas lights, the furnace warms up, the blower starts then abruptly the gas cuts off.
  36. Problem: The fuse on my control board blows constantly. How do I find where the short is?

32 thoughts on “Furnace troubleshooting questions with answers index

  1. Hi, I have a Coleman Evcon EB12E electric furnance. My problem is The fan will automatically come on, but the elements will not come on unless, I turn the thermostat up a few degrees, when the room gets warm the elements turn off but the fan continues to blow and if left blowing it blows cold air, so I have to turn the thermostat down to turn the fan off. I have replaced the the sequence switch, and that didnt solve the problem. Your help would be greatly appreciated.

    1. Hi Kathy! This sounds like you might have a thermostat problem since you said that the heating elements will not come on until you turn the thermostat up a few degrees. If you have a W1 and a W2 on the thermostat then maybe the W1 set of heaters are not working and you only get heat when the W2 heaters are activated by the thermostat. The thermostat should send 24 to 28 volts AC through the “G” green thermostat wire to turn your fan relay or fan relay sequencer on to get the fan to turn on as soon as the thermostat senses the need for heat and turns on the blower. The “W” white thermostat wire should turn the electric heaters on. I would suggest making sure that you are not gettng 24 volts through the G wire when the thermostat is turned down where it should not be heating anymore. So you would test between G and C (com) to make sure you are not getting 24 volts to the fan relay sequencer when the thermostat is turned down where the heaters should not be coming on. Most electric heat thermostat are set to automatically turn the fan on through the G (green wire) when the electric heaters come on. Another thought is that maybe you have a W1 and a W2 on your thermostat connected to two levels of electric heaters and when the W2 heaters come on and you feel heat, but maybe the W1 bank of heaters are burnt out or have a problem so when the thermostat turns W1 heaters on all that you feel is cold air. If you have a W1 and W2 on your thermostat make sure both sets of electric heaters are working. Another thing to think about is that some of the sequencers have a long delay on them which could be 2 to 3 minutes. The sequencer should eventually shut the fan off after 2 or 3 minutes after the 24 volts is removed from the coil voltage of the sequencer by the thermostat. Here is a link to a real good Youtube video on how sequencers work. I hope this gives you some things to look for that might be the problem. Hope you can find and fix the problem soon! Steve

  2. put new control board in furnace the blower motor will only work when you put the fan on on thermostat it is a trane furnace

    1. Depending on how old your furnace is the control board usually times how long before the blower comes on in the heating mode. If you have an older furnace with a mechanical fan/limit control then this could be the problem. The mechanical fan/limit control could be broken. Please make sure that when you installed the new control board that you have one of the blower speed wires attached to the “Heat” connection on the control board if the board has a “Heat” designated terminal. I would think it is a control board problem if the board does not send 120 volts to the blower motor in the heating mode. I hope you can find and fix the problem. Steve

  3. I have a carrier gas furnace where the hot surface igniter will not work. Read on on your site on how to check it and found it was reading over 120 ohms and had a few white spots. I thought I had found the problem but no! After replacing it with a new identical one and turning everything back on, it starts to work as expected and it gets to the point where the gas starts but I do not see a glow from the hsi and after a few attempts it shows code 34 again. Any clues on what I should check next?

    1. Hi George! Sorry that you still can not get the ignitor to glow after replacing it with a new ignitor. I would like to suggest that you check to make sure all rollout switches, pressure switch and your limit switch is closed. We discuss this problem in a post we have on the following page: I hope that it is a simple as pushing in on one of the buttons on one of the rollouts and you do not need a control board. I would also suggest that you make sure all connections are good and tight on the control board and any other connections. I hope you can easily find and fix the problem. Please send me your product number if you would like for me to look up parts to our email address:

  4. I have an American Standard 2/4TEC air handler. When the furnace comes on to heat the blower comes on as normal but when the electric coils kick in I hear a buzzing noise that has gotten louder, sounds like a possible relay or transformer? The unit seems to be operating normally, just a very noisy buzzing sound. I can not find a wiring diagram for this unit.

    Model# 2TEC3F48A1000AA
    Serial# 6083X8U1V

    Please advise on what the issue might be. Thank you.

    1. Hi Ron! You might have a noisy sequencer or circuit breaker. I would suggest turning off all the power and checking to make sure all the high voltage wires are good and tight. A circuit breaker that is arcing (going bad) can cause a noise like you describe. You might try taking the cover off your air handler and see if you can tell where the noise is coming from. You can usually tell if it is a transformer that is buzzing. Sometimes just tightening a transformer down with help stop the noise. I would not suggest running with the cover over for more than a couple of minutes because if you have a heat pump this could cause high head pressure which is not good for the outdoor heat pump. If you find a part that you need I will be glad to give you a part number. Steve

  5. Is there an easy way to clean some corrosion on a coil of the inside air handler ?

    1. Hi Jeff! No sir, I do not know of an easy way to clean an evaporator coil. We have a good video on the following page which shows how to clean a coil on the following page: I always removed the blower motor so it will not get damaged by water (if it is and up-flow furnace). Used coil cleaner, a spray bottle of water, a fin comb tool (to clean the fins) and a wet vac with a brush to clean the under side of the coil. Sorry that I do not know an easy way. I know that you will see a tremendous difference in air flow and better cooling if the coil is good and clean. Thanks for asking this question. Steve

  6. I have a Goodman GMV90905DXA that is about 12-13 years old and it runs fine. I was changing the filter and had the fan cover off and noticed a little bit of water in the rear corner of the fan section (opposite the motor/control board).

    I found that the issue is that at the bottom of the burner section water (condensate) is collecting on the flat metal bottom of the burner section. It is not coming from the plastic cover but it looks like it is coming from between the base of the burner unit and the bottom of the sheet metal (under the plastic cover). The condensate drains were working but I cleaned out the tubes/trap on the outside of the unit just to make sure. I have taken the burner section cover off and watched to see exactly where the leak is but when I am watching there is no leak (I let it run/watched for 30+ minutes) If I check the next day though there is a small puddle on the base of the burner unit about 3-4 inches in diameter on the far left side and a quarter size rust spot (which makes me think it has been going on for a while). I would appreciate any insight you may have on what this is and what to do to fix it before it creates a really big problem. There is no leaking on the outside of the unit and no issues with it starting, running, etc. – Thanks

    1. Hi John! This sounds like it could be a secondary heat ex-changer leak. About the only way I found to find leaks in secondary heat exchangers is to take the blower out and take a look at the secondary heat exchanger. Several times I have had to replace rubber hoses that come off the heat ex-changer or replace the secondary heat ex-changer completely. The heat ex-changer should have a life-time warranty. It is a pain replacing it because on the ones I replaced the hole front of the furnace has to be removed. You might want to have a tech check this problem out. Of course they will want to sell you a new furnace. I hope you can easily find and fix the problem. Steve

  7. Hello,
    I like your website . Lots of info
    I have 2 level Goodman hvac system . My upstairs heating works fine . My
    Downstairs heating has stopped working . I saw the upstairs furnace in the attic.
    I cannot find the downstairs furnace . I cannot find it . There are two condenser
    Units outside the house . I also have crawlspace with ducts inside . How do I fix
    My heating problem downstairs . The system is 12 years old .
    Thank you for your help .

    1. Hi! If your duct work is in the downstairs floor then more than likely your downstairs furnace is located in the crawl space. You will definitely need to find the downstairs furnace in order to work on it. When you do find it…We have lots of furnace troubleshooting advice on the following page: I would suggest going through the troubleshooting flow chart to see what is wrong: We also have lots of troubleshooting questions and answers on the following page: If you have any specific questions please let me know. Thanks! I hope you can easily find and fix the problem. Steve


    1. Hi Mr. Bray! The part number for blower motors are usually located on the motor label which is glued to the motor body. I hope you have a great day! Steve

  9. I hear water sloshing in drainage tube while heat is on electric furnace.

    1. Hi Mr. West! If it is actually water that you are hearing then I would suggest trying to blow the drain tube out with compressed air. I am sorry, but I really do not know anything much else to recommend.

  10. Hi. I have a two year old white Rogers gas valve on my furnace. The pilot lights and stays lit but burners don’t. Tried bypassing thermostat..nothing happens. Turned valve to off, pilot stays lit. Disconnected electric, pilot stays lit. Had to turn gas off completely for pilot to go out. Wassup with that?

    1. Hi Neal! Standing pilot furnaces usually have a thermocouple which senses the pilot flame. We discuss how this works on the following page: The pilot flame will continue to burn until the flame is blown out and the thermocouple cools down. I would suggest that you test the gas valve with a volt meter. Set your thermostat so it is calling for heat with the pilot lit. Test the wires going into the gas valve to see if you are getting 24 to 28 volts to the gas valve if you are and the gas valve is not opening then you have a gas valve problem. If you aren’t getting 24 volts to the gas valve then you could have a thermostat problem, thermostat wire problem, limit, pressure switch or roll-out switch could be open or a low voltage transformer problem. We have a troubleshooting flow chart that I hope will help you out on the following page: I hope you can easily find and fix the problem. Steve

  11. I have a Goodman AC/propane heater combo. It is 12 years old. What happens is when it calls for heat the blower comes on. after a short time the ignitor causes the first burner tube to fire, (it is a 3 burner tube set up), but the next two tubes fail to fire causing the sensor to shut it down. I have manually ignited the next two tubs and it works perfectly. I usually manually ignite the last tube and when I do that the middle tube will fire. The unit is a goodman, model # PGJ0420751A. I have not cleaned any of the three orfces yet. The fact that I can manually light the burners tells me propane is coming through. I have only guessing but the three flames all seem to be of the same intensity.

    1. Hi Mr. Robinson! This sounds like either the gas runner between the burner tubes is dirty or stopped up or you do not have enough gas pressure to ignite the other two burners properly. LP Gas is very critical on getting the right pressure to burn correctly. This should be adjusted with a manometer. Here is what I found when I Googled the subject: I would also check the orifices to make sure they are not clogged up too. I would start by turning off the power to your unit and blowing out the burners and gas runner with compressed air. I hope this fixes your problem. Steve

      1. Thank you Steve, I just noticed the runner between the burners and they did not seem to be lit. I am guessing I can blow then out without removing the burner unit. I am having a tech come out tomorrow and check if I have the correct pressure at the Propane tank regulator and the regulator at the house. I was concerned I did not have pressure also. We shall see. I will let you know the results. Again thank you. Boyd Robinson

      2. Hi Mr. Robinson! I hope that the cleaning and the gas pressure adjustments fix your problem. Please let me know when you find out what the problem was. Thanks! Steve

  12. my daughter made thee part of a plug piece that fits togethr bitsbthe plug piece go down thee vent in her bedroom how do i get it out

    1. Hi Terry! If the plug is not too far down the vent I would suggest using a vet vac with a long hose to try and retrieve the piece out of the vent. Sometimes a small mirror and a flash light might help you in viewing the lost piece. If the piece slipped too far into the vent to use a wet vac then you might have to take the vents (duct work) apart to retrieve the lost plug. I have you can get it with a wet vac. Best of luck! Steve

    2. Steve, Boyd Robinson here, I don’t know if this will be on the right post or not, but my problem was the dirty runner between the 1st and 2nd burner, and the 2nd and the 3rd burner. Rust mostly, cleaned out the opening and works fine. Thank you for your help. I had been having problems for two years and then it just quit working.

      1. Hi Mr. Boyd! Glad to hear that you fixed your furnace by cleaning the dirty rusty runner between the burners! Thank you so very much for letting us know this fixed your problem. I hope it will help others out in fixing their furnaces. Thank you so very much for posting this! Steve

  13. it s winter, upper mich, my ladyfreind sets her furnace at 60! the temp inside is 59 the furnace kicks in but does not blow heat, shuts down, and repeats another cycle the furnace works fine when its set above the inside temp of the home, what damage will this cause to the furnace , if any ?

    1. Hi Mr. Scheiding! Thanks so much for asking this question. It is not good for the parts inside the furnace to short cycle. Parts have just so many cycles in them. The short cycling can cause premature failure. Wow! 60 is pretty cold! The thermostat might not be programed to go that cold. Of course, you would need to determine what is causing the short cycling. Is this a thermostat problem, a flame sensing problem etc? We have a furnace troubleshooting flow chart that should help you find the problem on the following page: We have lots of furnace questions and answers on the following page: I would suggest starting my testing between W and C (com) on the furnace control board to see if the thermostat is cutting the furnace off and on. Please make sure you are getting a constant 24 to 28 volts AC between the W and C (com) terminals on the control board when the thermostat is calling for heat. If you aren’t then this is a thermostat problem. If it is a thermostat problem then you would need to get a new thermostat or try to set the thermostat degree difference or anticipator up so the themostat keeps the furnace on longer. If this is a flame sensor problem I would suggest trying to clean the flame sensor. I hope you can easily find and fix the problem. I hope you have a blessed day! Steve

  14. I have a Carrier 1986 Model 58GS100-150CA furnace. Lately the main burner ignites and then immediately shuts off then re-ignites several cycles. Finally it will remain on and run normally. I cannot locate a flame sensor on this unit. I do not believe it has one. So what else could cause this problem?

    1. Hi Mike! This could be something as simple as a dirty 3-wire pilot burner. I would suggest that you try to clean the 3- wire pilot burner out with compressed air. Our Carrier parts program shows that your furnace uses the LH680005 three wire pilot burner that we sell on the following page: I hope that cleaning the pilot burner fixes your problem. If not you might need a new pilot burner. I would also recommend that you check are wire connections and grounds to make sure they are good and tight. Steve

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