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FAQs on why the forced air heating or cooling air handler troubleshooting: blower fan won't shut off:
Frequently-asked questions about what to do when the furnace blower or air conditioning blower fan won't stop running when it should.
This article series describes what to check if the furnace or forced air blower fan does not stop when you expect it to do so
. These same diagnostics also aid in air conditioning blower assembly diagnosis when an A/C blower continues running. We explain what switches or controls may be set improperly or what else, such as a shorted wire, can cause continuous HVAC fan operation.
Questions & answers about why a furnace blower fan does not stop when you think it should are discussed here. These questions and answers were posted originally at FURNACE FAN WONT STOP - be sure that you check that article for help in diagnosing a furnace fan or blower that doesn't stop running.
Remember to check that the FAN ON switch is not set to ON at your thermostat and that the FAN ON switch is not set to ON at the fan limit control in your heating furnace or air conditioner (if your control there includes that feature).
On 2016-12-22 by (mod) - fan sometimes kept running more than one hour after burner has been automatically shutdown
Running the fan for an hour after the burner has shut down means something's wrong. I suspect a bad wire connection or a failing limit control.
The fact that the problem is intermittent also suggests the same diagnosis. If there's no obvious loose wire or loose connection I'd ask for help from a service tech.
On 2016-12-22 by Anonymous
My fan sometimes kept running more than one hour after burner has been automatically shutdown, sometimes the fan stopped just a few minutes after the burner is shutdown.
Is this a problem with the fan limit switch which should tell the blower to turn off when the residual heat in the furnace is dropped to below the temperature setting? Or is just malfunctioning?
On 2016-12-16 by LukeDoes anyone can tell me what is best;continuous 'auto'mode or intermittent ? We have crazy cold winters here and it would start every other 15 mins on ON/OFF mode and no idea if that'd be bad for the the furnace. Thanks
On 2016-12-11 by (mod) - Furnace blower keep running without thermostat turn onmost likely the problem is one of those listed in the article above.
On 2016-12-11 by VivekFurnace blower keep running without thermostat turn on
On 2016-12-04 by BillThe fan runs perfectly in the AC mode and in manual but will not start when the fan control reaches the desired set point. The gas valve stay open until the plenum reaches the high limit set point then shuts off.
On 2016-10-09 by Beckywhat would we check on when the fan does not shut off after the heat is reached. We have a lennox whispter heat furnance. We don't know it its in the thermostat or has something to do with the furnace it self.
On 2016-10-06 by MattGreat article! Couldn't get my hunting camps furnace fan to shut off. The post led me to the fan limit control switch in manual mode. Easy fix with the article and about to call a tech. Thanks!
On 2016-09-21 6 by Mike
Even when my thermostat has the heat/cool switch to off and the fan to Auto, the fan occasionally comes on and then shuts off after a few min (maybe total 5-10 times a day). With heat/cool off, I expect the fan would NOT come on at all.
When I completely disconnect the thermostat, the fan does not come on at all. I changed the green and red wires within the same 18/7 thermostat wire, hoping it was just those two that might be the culprit but it still occurring. Furthermore, I changed the thermostat, same issue occurring. Any ideas?
On 2016-09-05 by rajesh
My lg 1.5 split Ac was indoor blower motor capacitor was 2mfd I go changed 2.5mfd comes any problem or not tel sir ( and same problem is 10hr cotune running motor in out of place spearat and will be stop what the reason...and I'll changed two new indoor motor same problem
My lg 1.5 split Ac was indoor blower motor capacitor was 2 I go changed 2.5 comes any problem or not tel sir ( and same problem is 10hr cotune running motor in out of place spearat and will be stop what the reason
On 2016-07-30 by (mod) - how to make the blower fan run constantly - by choice
Take a look at the switches discussed in FAN LIMIT SWITCH where you'll see an article section titled "Which Way to Set the White AUTO / MANUAL Fan Control Switch"
and then look at your thermostat after reading FAN ON AUTO MAN Thermostat Switch as you may also have a FAN ON switch on your thermostat.
Any of those controls can force the fan to run continuously
On 2016-07-30 by DavidI need to have the blower run constantly. What can I do?
On 2016-07-24 by (mod) - My air handler runs 24/7 regardless of thermostat settingCHeck the thermostat to see if the fan switch is in FAN or FAN ON position.
On 2016-07-24 by kurt
I have a PAYNE model # PFIMNC037 air handler and a totaline thermostat.
My air handler runs 24/7 regardless of thermostat setting (i.e., on off auto)I have even shut unit off at ckt brkr, removed electronic front panel of thermostat and reset ckt brkr and air handler still runs continously
On 2016-05-30 1 by (mod) - blower motor stops running after 10-15 minutesPerhaps an overheating motor
On 2016-05-30 by Fazilblower motor is running gud an. after 10 r 15 mins blower stop working. An again working gud. Wat a reason for this problem
On 2016-05-03 by KeithI have a Model: GPC1342H41AA
On 2016-03-16 by (mod) - Turns out. I had switched the control to continuous.>Thanks for the feedback John. Indeed it's easy to accidentally bump or change a control button such as the manual FAN ON switch on a limit control.
On 2016-03-16 by John DAfter I bled the oil line. The fan kept running. Turns out. I had switched the control to continuous. Also dirty filter and fan door left open. She runs fine now. Just follow these instructions and be patient. U should find the problem.this page really helped me.!
On 2016-02-12 by (mod)First disconnect the thermostat wires at the furnace side of the thermostat circuit to rule out TT wires shorted together.
On 2016-02-12 by Jaythere is a mobile home furnace electric furnace the fan will run non stop I took the thermostat off the wall it still runs all the wiring is correct I would just like some information on what to check to make sure I even changed the fan relay
On 2016-02-08 by (mod) - My furnace blower stops only when is in emergency heatAnon:
On 2016-02-08 by AnonymousMy furnace blower stops only when is in emergency heat but won't stops when is in auxyliary heat
On 2016-02-08 by osmanSo helpfull
On 2016-02-06 by (mod) - blowers runs continuous after power failureThanks Dan - that's odd. Typically a reset-button is designed to turn a device OFF in the event that it is not working properly. It's unusual to hear of a reset button that keeps a blower on when it shouldn't.
On 2016-02-06 by DanIt was a reset button I didn't see on top of unit, I checked the controls board, no bad marks on it, anyway it's good to go, thnx
On 2016-02-06 by (mod) - blowers runs continuous after power failureLook for a bad control board.
On 2016-02-06 by Danny MorrisI have an issue with a Coleman HVAC trailer closet unit, blowers runs continuous after power failure in the area, flashes shows open limit switch but both upper,lower switches show continuity , noticed that mercury thermostat does not show spark either way rotated
On 2016-01-24 by (mod)Where did you disconnect the thermostat: if you disconnect it at the furnace end, that's good for eliminating the thermostat as the problem. If you disconnected at the thermostat end the wires could be shorted together anywhere enroute.
On 2016-01-23 by Thomas 1848
I have a goodman gas furnace with a the same problem, the fan will not stop running. The thermostat is completely disconnected,the fan limit switch opens and closes and all the auxiliary limit switches are all good.
Still the fan stays on. When the power (bulk wire) is disconnected and reconnected the inducer motor comes on but goes off after a few seconds but the blower motor stays on.
Circuit board still indicates open fan limit switch but it's good.
I do notice that there is no ground on the circuit coming to the furnace 115v wiring.
Could this be the problem!?
On 2016-01-10 by AnonymousMy furnace continues to run after the room temperature is higher than the set temperature of thermostat. What might be the problem?
On 2016-01-09 by (mod) - check the backup electric heating elements in the furnace of a heat pump systemThanks Larry for the good suggestion: a fan control wire or even possibly a thermostat wire shorted to ground (the metal furnace or blower compartment body) should be on our checklist.
On 2016-01-09 by LarryPull electric elements out of furnace and make sure none are touching the frame of the furnace. I found this condition on a goodman that had the elements and the fan running all the time .
On 2016-01-07 by (mod) - can't turn off the blower
Fred, if you made your test with the thermostat wires completely disconnected then I agree that the problem is probably a control board or relay.
Just be sure that the manual fan on - off switch is in the off position ... if your unit has that switch.
On 2016-01-06 by fredelectric air handler ( carrier ) runs continuously engageing heaters with thermostat off only way to stop running is to knock breaker don't know if it is sequencer or fan control board checked sequencer with power off and it checked good
On 2015-12-17 by GennaroFan running all the time, and switch off
On 2015-12-16 by (mod) - Fan running all the timeAnon:
On 2015-12-16 by AnonymousFan running all the time
On 2015-12-12 by (mod)Mike
On 2015-12-10 by Michaelangelo
My blower does not shut off even after I disconnected all the wires at the thermostat and the green wire in the furnace. I can't even find the limit switch. I've looked high and low around the furnace including where the blower is located but to no avail.
I can shut off the blower from the emergency switch and turn on as well from there. Heck I can't even shut off the blower from the breaker. I'm so stumped. Any ideas what could be causing this fiasco?
On 2015-12-06 by (mod) - Furnace fan won't stop unless I turn it off at the breaker.CHeck to see if the manual FAN ON switch is on at the thermostat or at the fan limit switch.
On 2015-12-06 by CindyFurnace fan won't stop unless I turn it off at the breaker. Replaced thermostat and before I could get past the setup instructions the fan was on again. Our home & unit are only 3 yrs old. What should I look for???
On 2015-11-21 by (mod)Bernie, I don't understand your system. If we are heating occupied space typically the thermostat that calls for heat is monitoring temperature inside that occupied space. Monitoring outdoor temps is used for some systems to adjust boiler temperature for efficiency reasons but not to turn heat in the building on and off.
On 2015-11-20 by bernie
The amount of heat generated is predicated on the gauges outside of the building that monitor the temperature.
I had the staff check it this
morning and it is functioning properly. We have it set higher than
recommended does this sound accurate because when it is below 55 we have not heat
On 2015-10-14 by (mod)Thanks for the feedaback, Happy, that should help other readers.
On 2015-10-14 by Happy Again
We recently purchased a Honeywell thermostat and once installed the furnace fan would not shut off and I checked this website for help.
After a few days of frsutration, my husband took a look at the modular on the furnace that connects to the thermostat and found that the black wire was connected to the green selinoid so he turned off the furnace and installed the Honeywell thermostat so the black wire was connected to the green selinoid and the fan now works as it should.
On 2015-09-29 15:33:34.602060 by dowzer man)I HAVE APACKAGE UNIT THE BLOWER FAN WANT COME ON WHEN THE CONPRESER COMES.ON NEED HELP
On 2015-09-24 by (mod) - My fan won't shut off.After disconnecting the thermostat entirely at the fan if it keeps running there is either a fan on switch in the air handler or a bad control board or relay.
On 2015-09-24 by MattMy fan won't shut off. Replaced thermostat and ran new thermostat wire with the same result. Should I replace the relay board in the air handler first or the limit switch? Thank you
On 2015-08-20 by Mdk8998We disconnected the thermostat completely, checking the two wires that connect it. They appear fine at the wall.
We left the thermostat off the wall, bare wires, thinking to order a new one and...and the furnace fan came on. Guess we don't need a thermostat. Now what can we check?
On 2015-08-18 by (mod) - My furnace comes on and runs cool air (we don't have AC) even when I have it in the OFF position ofCheck for thermostat wires shorted together
On 2015-08-18 20:21:57.849267 by Mdk 8998My furnace comes on and runs cool air (we don't have AC) even when I have it in the OFF position of <heat off air> and the auto/ manual fan is in the auto position. I have the temperature set all the way down to 50 degrees. Where do we start looking?
On 2015-08-08 21:46:16.455005 by (mod) - Our fan has been running continuously for the past 12 months.Denny
On 2015-08-08 17:56:55.264352 by DennyT
Our fan has been running continuously for the past 12 months. We have a heat pump & central AC unit.
Goodman 4 ton. We just had the unit replaced and the fan is still running constantly. The heater/AC company will no longer attempt to figure it out an states that it is the way the unit was designed to run.
This is the same unit that we had previous to replacement and up until the last year the fan turned on & off. If I raise/lower the setting by one degree, the fan will shut off until the unit kicks back on. It quickly comes to temp and we had a second guy confirm this was the right size unit. I have come to manually shut it down during the evenings as the fan noise irritates me.
The other night, I didn't have my glasses on and accidentally hit something and the screen went blank. By the time I came back with my glasses, it was back on.
(The heater guy had previously hard reset the thermostat and it didn't help). Since hitting the wrong spot on the digital honeywell thermostat, the fan has been turning on and off as it should.
Do you think it was just a setting that needed to be reset or do you think we need a new thermostat? The thermostat is approx. 8 yrs old. I greatly appreciate anyone's thoughts or suggestions!
On 2015-02-19 23:32:18.317540 by (mod) - Furnace turns on and blows heat for few minutes or hoursCheck for a loose wire, especially in the thermostat circuit.
On 2015-02-19 22:57:10.506660 by Anonymous
My Furnace turns on and blows heat for few minutes or hours. Don't know it does it randomly where some time goes days with out turning off and some days in hours it turns off. Heat stops blowing warm air...and then only blows cold air.
Even turning off thermostat it still blows cold air..I turn of main switch and reset the saftey switch..and comes back on to go off at some random time next time..what could cause that. it causes the saftey switch to flip blowing only cold air till main power turned off or reset saftey switch..
On 2015-02-19 14:35:19.313360 by gregfan will not shut off when the heat does?
On 2015-01-12 14:08:59.068940 by (mod)Check for shorted thermostat wires.
On 2015-01-12 04:00:24.039020 by Hankmy hvac unit runs when the thermostat is turned off and fan is off. this happens when it seems that the humidity rises.
On 2015-01-10 02:52:04.548520 by Alexfan motor run . light blinking 6 time
On 2014-12-10 01:36:48.366850 by (mod) - we need to replace our limit switch as the fan is continuously runningAmanda
On 2014-12-09 22:11:35.180820 by Amanda
We just found out that we need to replace our limit switch as the fan is continuously running. I have found one online and will be ordering it, but I have a question about the other limit switch. The small button style one with two wires attached, the high temp limit thermostat.
When looking at the furnace for the source of our problem, I kind of broke the button one free of the built in frame. I'm looking to replace that and am having no luck searching the part number located on it, but I have found one with the correct Limit of 300. The only difference is this one has a manual reset button in the center of it, which our current one does not. Is this really an issue?
Can I use the one with the manual reset in place of one without it? As long as the measurements are the same?
On 2014-12-01 02:49:20.556870 by (mod)Quite right, Ray. That fan run-on interval after the burner shuts off is important to avoid cracking a heat exchanger.
On 2014-12-01 00:35:49.157730 by Ray GThanks for the input Dan, I have a new switch on order as I type this. and am making sure the fan runs for a bit after the furnace shuts off, in order to cool the heater box down before shutting off.
On 2014-11-28 23:37:41.321540 by (mod) - Ray's Fan Limit Switch Problem Troubleshooting TipsRay you did a steller job of debugging a fan limit switch problem.
On 2014-11-28 22:46:55.592780 by RAY G
After lighting my furnace, the fan kept running and would not stop. After several hours of troubleshooting and following the schematics. I traced it down to my fan limit switch. I removed the switch and found it to be stuck at the on -150 position.
I cycled it by hand a few times and took a wire brush to the base. it had some build up causing it to not release to the off position. After cycling it the switch ended up going back to the off position. I installed it and my furnace now works fine. Great pictures on this site made it possible for me to fix it myself. Thanks!!
On 2014-11-24 22:46:17.637740 by (mod)Anon, if you turn off the blower fan on a heating furnace the unit's fan limit switch should shut the system down. If it does not,mourn off all power to the equipment and call for a repair tech.
On 2014-11-24 22:43:37.886180 by (mod)Selena, set the thermostat to below room temperature. If the heater does not stop after a minute or two, shut off its electrical power and call your heating service tech for repairs.
On 2014-11-24 03:42:17.575860 by AnonymousWill it be dangerous if we stop the AC blower fan switch and stop the furnace ? will it effect the air circulation in the house ?
On 2014-11-11 01:21:50.344570 by selenaWhat should I do my burners keep burning and my blowers keep blowing? Thank you
On 2014-10-28 14:33:49.035130 by Anonymousi have 3 settings on my heater/ air conditioning fan 1on, 2 crc, 3 auto. the fan seems to be on all the time, whether i set it to auto or circ. i don't use the on setting. which will only let the fan on when the heater or air is engaged?
On 2014-10-12 17:36:13.598490 by MikeI just checked again after leaving it for the night and the dial is still stuck at 150?
On 2014-10-12 02:31:48.643290 by Mike
Hi.. I just got the oil burner in my garage up and running after not being used for a couple years. The fan will kick In a free warming up and you can see the dial on the limit switch move as it warms but it won't shut off.
Even after 30 minutes or so the dial on the limit switch won't move back down and shut off the fan. If I turn the dial manually it will shut the fan off though. Bad limit switch?
On 2014-10-06 21:23:14.406250 by AnonymousOK Thanks
On 2014-10-06 21:20:29.998540 by (mod) - fan stops only if I tap the limit switchAnon
On 2014-10-06 21:12:57.701990 by Anonymousthe fan starts ok, but keeps running until I tap the limit switch. Have to do this each time or fan keeps running. Is the limit switch bad?
On 2014-09-12 03:11:47.073400 by (mod) - Is it possible for me to add a second switch in parallel with the over ride button outside the furnace - DO NOT DO THISNo Woolf,
On 2014-09-09 19:02:40.368690 by Woolf
I have a standard domestic gas furnace. The remote thermostat has only a 2 wire run back to the furnace.
I wish to run the furnace blower for long periods to circulate cooler air through the house during the summer. I can push the manual over ride button in on the high limit switch, which achieves this.
Is it possible for me to add a second switch in parallel with the over ride button outside the furnace so that I don't need to open up the furnace to operate it? Is this a safe practice?
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