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Problem: Your fan on your furnace runs all the time and will not shut off

Problem: Fan on your furnace runs all the time and will not shut off


1. Check to make sure the fan is not in the fan “ON” position on your thermostat.

2. If your furnace goes off on high limit or if one of the rollout switches are open then the furnace fan will run all the time because the furnace control board is telling the furnace that the furnace has over-heated and the fan runs to cool the furnace down. Check to make sure the limit and rollouts are all closed. You will need a volt meter to test. We sell a good volt meter on the following page: Please click here for a real good meter and testing instrument. You might want to purchase an less expensive volt meter from Radio Shack, Walmart, Home Depot.

3.  Check to make sure your air conditioning fan relay or control board fan relay is not stuck or welded in the on position. The contacts on your air conditioning fan center relay or control board could be welded closed, causing the fan to run all the time. You might try lightly tapping on the Air conditioning fan relay to see if the fan will go off? We sell Fan Center Relays on the following page: Please click here for fan center relays.  Many of the new furnaces have the control board control the fan off and on timing. If you would like for us to see what control board your furnace or air handler uses please email anytime at: We have programs where we can look up parts.

4. Please make sure you are not getting 24 to 28 volts AC between the G (green) and C (common) wires on your control board. Set your thermostat to “Fan Auto”.  Your thermostat should not be calling for heating or cooling.  If you are getting 24 volts between the G (green) and C (com) thermostat wires on your control board then you might have a bad thermostat or shorted thermostat wires.  You should only get 24 volts between G and C when the fan is set to “ON” or if the air conditioner is turned on.

5. Sometimes the fan limit control or rollout switches will  stick open. You might need a new fan limit control. On many of the rollout switches they are manual reset and all you have to do is press a button on the switch in. I have been on many service calls when all that I had to do was press a button in on the rollout. The rollouts and limits are safety devices to protect you and your family. Please make sure you see why the limit or rollout has opened up. Most of the time limits and rollouts open because the furnace has over-heated. Sometimes the heat exchanger is leaking or the vent is stopped up and you will need to have an HVAC Tech inspect to see why the limit or rollout opened. This can be a dangerous condition for you and your family.  You might need a new Fan Limit control. There are many different types of controls. We sell some fan limit controls and rollout switches on the following page: Please click here to see our limits and rollout switches page. Please send us your furnace’s model number if you would like for us to look it up and see which limit and rollouts your furnace uses. We would love to try and help you out!

We have a YouTube video that Acservicetech was kind enough to make which shows how to troubleshoot this problem with the fan on a furnace that will not shut off. Thanks Acservicetech for taking the time to make this video!

39 thoughts on “Problem: Your fan on your furnace runs all the time and will not shut off

  1. Hi Steve
    i have same problem fan running none stop manual set the light flashing 4 times cause limit switch bad, but I replacement high & low limit switch no luck. Please advise

    1. Hi John! If you haven’t make sure all your rollout switches are closed. Sometimes furnaces have as many as 5 or 6 rollout switches. Some of the rollout switches can be hidden like under or on top of the blower motor housing. There is a really good YouTube video at the bottom of this post that shows how to troubleshoot the furnace if the fan will not shut off. I hope the video helps you find and fix the problem soon! Steve

  2. Hi Nemo, I saw several posts from you and I am having the very same problem…were you able to figure out the problem?

  3. Hi, I have a heat exchanger drop for outside wood burner with nothing but the radiator water type exchanger in it and the blower and blower control box to the thermostat. As of late the blower motor would continuously go after the thermostat had opened up. If I closed it and opened it real fast the blower motor would shut off after several attempts. I change the relay and it worked for a day and a half and now it’s staying on again. There are no fan limit switch or any of the other devices that a gas furnace might use. What could possibly be the problem?

    1. Hi Alan! I would hope that there is some kind of limit on your wood burner furnace so that it does not overheat. Sounds like you might have a low voltage problem. If the relay only worked for a day and a half I would make sure that the relay is getting a minimum of 24 volts to the relay coil. If the relay is getting low voltage, below 24 volts it will cause chatter within the relay, which causes arcing within the relay and premature failure. I would recommend checking the relay coil to make sure all connections are tight and the relay is getting a minimum of 24 volts. If it is not getting 24 volts then you might have a weak low voltage transformer, bad thermostat wires, or thermostat problem. If your thermostat uses batteries make sure the batteries are in good condition. Make sure all wire connections both high and low voltage are good and tight. I am sorry, but I am not familiar with the set up on wood-burning stoves. It sounds like your blower is on all the time when the thermostat is calling for heat and off when the thermostat is satisfied. So if the blower is staying on I would recommend checking the thermostat, thermostat wiring and low voltage controls. I hope you can easily find and fix the problem. Steve

  4. Hi Steve,
    I have the same issue of blower fan running constantly, even if I disconnect thermostat or control board. I believe I have an ECM x13 motor, 1/2 hp 230vac, the ones that have power supply all the time but only turns on when signaled (Genteq/Endura FM19). There are 5 pins for signaling (24v) and 4 pins for power supply (c, 115v, G, 115v). If I disconnect the 5-pin connector it would still run constantly. Interior of the ECM module looks perfect, capacitors, wires, seals, all good. What could be the problem here?

    1. Hi Nemo! I am sorry, I do not know what the problem could be without an ECM motor analyzer. Sorry that I can not give you any help or recommendations. Most of the time the motor module is at fault, but if you want to prove that the motor module is at fault you would need an analyzer. Steve

      1. Thank you very much for the reply. Regards, Nemo

  5. Hi, I have an Air Condition System where the evaporator fan motor runs continuously and will not shut off unless I turn the breaker on the system. It has been running fine but for the last month the fan will not shut off even when the desired temperature is reached and the outdoor unit shuts off.
    Your help would be greatly appreciated.

    1. Hi Banabas! This could be caused by any one of several problems. One you could have a blower fan relay on the control board that is stuck closed and keeping the blower fan on all the time. This could be a thermostat wire problem where the red and green wire has shorted together and it is keeping the fan on all the time. This could be a thermostat problem which is sending 24 volts AC through the green “G” connection on the thermostat to keep the fan on all the time or it could be a limit or a rollout switch that is open which tells the control board that the furnace has overheated and telling the fan to run all the time because a limit or rollout is open. You will need to check with a voltmeter to see where the problem is located. Without a voltmeter to test it would be a guess as to where the problem is located. I hope you can easily find and fix the problem. Steve

  6. Please help! I have a old split system in my house. The Inside unit blows hot air and will not turn off unless i turn the breaker off. I was told it could be the thermostat so i went and purchased a brand new thermostat that is fine for my system as it said it has the emergency heat. So that did not help. I was then told to try the capacitor and contactor to the condenser and that did not help. Please reply any advice will help at this point.

    1. Hi Steve! I am guessing that you have a heat pump since you said something about “Emergency Heat”. This sounds like you have a stuck sequencer or relay if you have electric heat. I am guessing that you have a heat pump and auxiliary electric heat backup. If you do have a heat pump and electric heat back up you will need to use a voltmeter or better yet and Amprobe to see which sequencer or relay is stuck and keeping the heat on. You could also have a shorted thermostat wire that is causing this problem. I hope you can easily find and fix the problem. Steve

  7. Hello – I hope this finds you well. Unfortunately my heat pump/air exchanger is not. I have a carrier FX4BN030. We had sever weather and likely a lighting strike nearby. I came home to the AC blowing hot air and a TV that no longer turns on. The AC outside compressor and fan was not running. The blower runs and there is nothing I can do other than cutting power to the exchanger or removing the low voltage fuse to make it stop. Do heatpump go into a default auxiliary heat mode when certain components fail. I assume the heating element was energized as the air blowing out f the vents was hot – though the room temperature was 92 – the air felt hot.

    1. Hi Mike! So very sorry that more than like your home was hit by lightning! More than like you had a power surge and it could have messed up any of the low voltage components of your heat pump system. You will need to do some testing with a voltmeter to see what is happening. If you are not familiar with reading electrical circuits then I would suggest you call in an HVAC company to troubleshoot. Most lightning strikes are covered by insurance. You would need a statement from your HVAC company showing that you had a lightning strike. This power surge from the lighting could have messed up your thermostat, control board in your air handler, contactor on your outdoor unit and the reversing valve solenoid. Anything that runs off 24 volts. It might only be one component that is messed up hopefully. I looked the part number up for the control board for your air handler and the part number is HK61EA006. Without testing it would be a guess as to what is wrong. Sorry that I can not be of much help. Steve

  8. Hello! I have a York model number ahp24b3xn21a furnace. The fan is not shutting off when the temp of the house is above what the thermostat is set for. It turns on fine when the thermostat tells it to, blows fine and the heat stops once the set temp is reached but the fan keeps running. Once it’s blowing cold air, I can go to the breaker box, shut off the breaker which stops it of course, turn the breaker back on and then it’ll stay off then until the thermostat tells it to start again. Thanks!

    1. Hi John! Did you check to see if your furnace is going off on limit during your heating cycle? I would suggest that you try to read the flash code on the control board the next time the blower stays on. Many times the control board will tell you what is causing the blower to run all the time. I would also make sure that you are not getting 24 volts between G green and C com on the control board. This would cause the fan to run all the time and would be caused by a faulty thermostat or shorted thermostat wires. I hope you can easily find and fix the problem. Steve

  9. Hi, I have a new Goodman air handler with a blower that will not come on unless thermostat cover is removed and breaker turned off then back on. As soon as the thermostat cover is replaced, blower shuts off. The first issue after install was the heat (probably just the blower) would not work. After checking wiring diagram, I found the wiring on fan relay were reversed. After correcting that, everything worked as it should. Now that it’s warming up, the same type issue is happening in ac mode.

    1. Hi John! I am sorry, I do not know what your problem could be without being there to test the thermostat and wires with a voltmeter. This sounds like you have a thermostat problem or thermostat wire problem. Some of the thermostats have a jumper on RH and RC. If your furnace does not have this jumper then you might need to add one. The fan relay should be energized through the “G” green thermostat wire. I would suggest that your check with a voltmeter to see if you are getting 24 volts between the G and C (com) wire when the thermostat is calling for cooling or if the fan is set to the “ON” position. If you are not getting 24 volts between G and C then you have either a thermostat problem or a thermostat wiring problem. If you are getting 24 volts between G and C and the fan is not running then you probably have a fan relay or air handler control board problem. I hope you can easily find and fix the problem. Steve

      1. The thing that’s puzzling me more than anything is that the fan will run when thermostat cover is off, but as soon as it’s replaced, blower will shut off. I’ll get it figured out and post an update. Thanks for the quick response!

      2. Thanks! I hope that you can get it figured out soon. Hope you have a great day and weekend! Steve

  10. Hey Steve , I’m hoping you can help point me in the right direction as I’ve had several HVAC companies try and fail to fix my problem granted most of them refuse to check any of the wiring and just keep throwing parts at it. I have a carrier 38ydb heat pump and a carrier fv4anf003 air handler controlled by a ecobee 4 thermostat. My current problem is when the thermostat calls for AC it act as normal and performs as expected until it hits the set point, at which time the thermostat shows no equipment running as it should but everything remains on ie. (Blower motor, compressor, the whole HVAC system as if the thermostat is still calling for it. But I can confirm it’s not calling for it any longer. I throw the service switch and it all powers down and the unit is fine with no equipment running until the thermostat calls for AC again. Now what I’ve done, I’ve replaced the thermostat THREE times now, replaced the PCB for the air handler, replaced the complete modular blower motor with new wiring harness, new heater kit as I had this same issue with heat staying on too. New condenser fan on heat pump and I did go through several transformers before this issue which I thought was fixed after I fused the secondary side. Now I’ve tried to check continuity on the thermostat wires, which seamed fine if I disconnected the wires on both sides. Have not checked the wires going to heat pump yet. I’m not a HVAC tech just a home owner getting tired of being told I just need a new system. Thank you so much in advance.

    1. Hi Bradley! I am so very sorry to hear how much time and money that you have used in trying to get your heat pump running right! Wow! I would suggest that you call Ecobee and tell them the problem that you are having. This sounds like a thermostat problem since everything is continuing to run even when the thermostat is not calling for cooling. I would suggest checking to see if you are getting 24 volts to the contactor coil when the outdoor unit continues to run. I would suggest taking the Y wire off the thermostat while the heat pump is running and see if your outdoor unit stops. If it does stop then it sounds like this is a thermostat problem. Yes, make sure that your thermostat wires are in good shape and not shorted out then try a higher VA low voltage transformer if you have not tried a new transformer with a 50 VA or higher VA. You might want to try a 75 VA transformer. I have had many questions from people who are having problems with their Nest thermostats. I have not had any questions about the Ecobbe thermostat. One person said that Nest tech support recommended a higher VA transformer which makes sense. If you are not getting enough voltage to run the system controls then nothing is going to work right. Here is a link to Amazon where they sell 75 VA transformers: I sure hope this solves your problem. Please let me know the solution to your problem so knowing the solution will help others. I know that you will find the solution soon! I love hearing how great you are in not giving up on this! I admire your persistence! I hope you have a great and blessed Easter! Steve

      1. Hey Steve
        First I want to say thank you for taking your time to read and respond to my question. So I am updating you I finally found my problem and wanted to share my experience. So I started off checking for voltage at the heat pump at the yellow wire to see what I was getting when the thermostat hit the set point and showed off but the compressor was still running. It was showing 18v. I pulled the wire there and it cut off as it should. So off to the store I went to get just a basic non programmable tstat. I wired it up leaving off stage two heating and cooling to just to see if I got basic function. Well to my surprise even the basic tstat was doing the exact same thing. So I dove into the wiring, to and from all the components tracing each one by one and boom there it was. Due to old system controls using a RS,RV style thermostat and had extra wiring running to the air handler for an old weather machine that was no longer attached but the wiring still existed tied in at the air handler and running into the wall where the old control board used to be, it had been taped up with electrical tape and the red, yellow,orange, and black had some how managed to touch back feeding the entire system since the last tech that had came and tied it back in at the air handler thinking it went to the heat pump. So this entire issue started with the installation of the new ecobee when a new 7 wire thermostat cable was ran to the system to replace the old RS,RV style cable. I can see why I was told many time it was the thermostat because it completed the circuit when installed and cause the short. Thankfully it is working now as it should with the same ecobee thermostat. Thanks again! Hope this can some how help someone else.

      2. Thanks so much for taking the time to let us know how you solved your furnace problem! Yes! I hope this will help others in the future! God bless you and your family today and always! Steve

  11. Hey Steve, I have an 80s model furnace that the blower motor continuously runs. this furnace has no control board, however it does have a fan control relay in an assembly with the transformer. I have replaced the fan relay and it continued to run constantly. since this wasn’t an emergency and the cool and heat still worked i left it how it was over the weekend. (it was in the 70s outside/76 inside on Friday) checking again this morning (in the 40s outside/63 inside) the blower motor is operating normally. I have 2 units that were having the same issues Friday that are no longer having those issues now that its cooled down, is there something Im missing?! I have a few years under my belt but i have not seen this before

    1. Hi! If your furnace has one of the old dial controls like in the following post: then you might need to adjust the “Fan ON” setting so the fan does not come on until the furnace heats up more. On a warm day, the control might be coming on if you have a pilot producing heat which could cause the control to heat up enough to come on. Also if your furnace is over-heating and going off on limit then this could cause the fan to run all the time. I would suggest that the next time the fan stays on to check the fan control and your thermostat connections (green wire) to see where the source of the power is coming from the keep the fan motor running. When you find the source you have found the problem. I hope you can easily find and fix the problem. Steve

  12. Hello.
    I have a two year old 5 ton Rheem heat pump. In the cooling mode everything works fine the inside fan turns off outside fan and compressor shuts off when it reaches the set point . In the heating mode everything works fine except when it reaches the set point and the compressor shuts off the inside fan will run all of the time. I changed my thermostat to a Honeywell RTH5160 series and followed the set up options and the fan still runs all the time in the heat mode after the compressor turns off and the set point is satisfied. With the new thermostat I tried to turn the fan to the on position and it will not turn on. I also tried to turn the thermostat to the off position and the fan would not turn off. The only time the fan will shut off is in the cooling mode. I have a stack able relay and I changed it with no results. I have not changed my board or the thermostat wire yet would that be my next step. Thank You

    1. Hi David! I would suggest that you test with a volt meter to see if the thermostat is sending 24 to 28 volts AC through the green wire. So you would set the thermostat to where the heat should be off and the fan not blowing air. If you are getting 24 volts AC between the G and C (com) thermostat wires then I would say you have a thermostat problem or a shorted thermostat wire problem. If you are not getting 24 volts through the green wire “G” then I would think you have an air handler control board or fan relay problem. You could also try removing the G green wire from the thermostat and see if the fan stops. If it stops then you have a thermostat problem. I hope you can easily find and fix the problem. Steve

  13. So my fan turns on then the igniter glows it fired a for a second then flamesstop and it keeps repeating every about 15 second with the fan staying on but won’t stay lit

    1. Hi Joshua! If you are referring to the fan as the draft inducer running then this would be normal as long as the thermostat is calling for heat. This sounds like you have a flame sensing problem. If you have not cleaned the flame sensor then I would suggest that you do that. We have a post about cleaning the flame sensor on the following page: If the blower motor is staying on then you might have an open limit, rollout, thermostat or thermostat wire shorted out. 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

  14. Had a new Goodman AC unit installed first month it ran ok but now when the inside temp reaches the cool set point, the inside units shuts off but the outside units stays running and sends out cold air and then I see frost start to build. Please advise

    1. Hi! More than likely the contactor contacts might be welded closed or one of your thermostat wires are wired wrong or shorted out. A thermostat can also cause this problem where the thermostat has failed to turn off the outdoor unit. We have a post about this problem on the following page: I hope you can easily find and fix the problem. Steve

  15. indoor fan motor runs quarter speed even after thermostat is in the off position

    1. Sounds like you possibly have a stuck relay on the control board that is keeping the fan running. I would suggest lightly tapping on some of the relays on the control board. If this does not work then you might need a new control board. I would suggest taking the green “G” wire off the control board to see if the fan still continues to run. A furnace limit that has opened up (furnace over-heated) will cause the fan to run continuously because the control board thinks the furnace has over-heated and needs to cool down. Please check your limit to make sure it is not open. I hope you can easily find the problem. If you want me to look up parts then please send your furnace’s model number to our gmail email account:

  16. heil gas furnace mod # nule 125 ak01 its used in a church i attend,we leave the thermostat set on 55 deg when not in use..but when we turn the thermostat up to 70 and it reaches 70 the blower fan motor turns off like it should after about 3 minutes .but when the heat cycles on again and the gas burner eventually turns off the blower fan motor runs all the time…is it the fan limit switch bad? it has a dial switch set at 100 deg off , 150 deg on and hi limit at 200 deg…thanks….

    1. Hi Mr. Collier!
      Thanks so much for your interest in our website! I would suggest that you watch the dial on the fan limit control and see if it moves below the 100 degree off setting. If it doesn’t move below that off setting then you might need a new fan limit. I would try changing the fan off to a higher temperature just to see if the control will turn off. I show how to adjust the fan on/off tabs on the following page: It looks from the parts list like your church furnace has a 5″ fan limit. Here is a screen shot showing the parts for your church furnace. We sell a 5″ fan limit control on the following page if this turns on to be the problem: I would also check to make sure that the thermostat is not sending 24 volts to the fan control. I would suggest testing with a meter between the G and C terminals to make sure there is not 24 volts coming to the control board from the thermostat causing the fan to run. If you do not have a meter you can remove the green wire from the control board to see if the fan stops. I would suggest making sure that all your limits and rollouts (if equipped) are staying closed. If one is open it will cause the fan to run all the time. Thanks so much for trying to help fix your church’s furnace and thanks for your service to God’s Kingdom. I hope you have a blessed day! Steve Arnold,

  17. I will be happy to try and answer any questions you have. Thanks so much for your interest and support in our website! Hope you have a blessed day! Steve

    1. Do you have the above translated in Spanish?

      1. Hi Rosa! No, I do not have our pages translated in Spanish. I thought that some of the browsers would do that for you. Here is a link to a page that explains this I hope: I hope that you can find something that helps. God bless you and your family today and always! Steve

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