FAQs on why the forced air heating or cooling air handler troubleshooting:

Set #2: What to check when an A/C or furnace blower fan won't shut off:

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.

FAQs on why the blower fan won't stop

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 2018-08-15 by (mod) - the thermostat is not precisely accurate

Sure the thermostat is not precisely accurate - it's not lab-grade precise.

But if just touching the dial by pushing the temp up - that means setting the temp another degree above the room temp - turns off the blower, then yes, then that sounds like a loose connection or wire or a failing control.

On 2018-08-12 by Bo

After my home reaches the temp. I set my thermostat to, the AC will shut off but the fan blower will continue to blow.

If I bump the temp on the thermostat up another degree, the blower will kick off. How can I make the blower kick off when the temp the thermostat is set to is reached?

On 2018-07-11 16:01:59.906237 by Anonymous

my blower motor continues to run with thermasta turned off

On 2018-05-11 17:09:41.455287 by Damo

Furnace is working fine but the AC fan will not shut off

On 2018-03-16 02:12:27.815335 by (mod) -

May

YOu need a service call to find out why the system is going off on safety-reset. The risk if you keep pressing the reset button is an accumulation of un-burned heating oil in the combustion chamber that can then get ignited in a puffback explosion.

Search InspectApedia for that phrase for something to read while you wait for your oil heat service tech to appear.

On 2018-03-13 16:52:05.033142 by May

my oil furnace runs to setting temperature, then stops until it calls click sound for heat again, the furnace try to run but it stops then the light is on. I have to wait for the house temperature goes lower then press the button, its back on again. then it keeps on and off like that. We did change oil filter, cad cell and nozzle. But its still not working. Please help. Thank you

On 2018-03-07 19:30:19.734735 by (mod) -

Ron

From just your note, I can't say when your fan should shut off. On most forced warm air heating systems the fan will run until the call for heat is satisfied at the thermostat, and for a brief period thereafter.

If the fan never turns off it's probably for one of the reasons listed in the article above on this page.

On 2018-03-07 19:28:56.410171 by (mod) -

Jim

Running the fan continuously should not damage the furnace, but it's true that some fan motors may be designed for continuous operation and others not

. I figure that if a furnace was provided by the manufacturer with a manual FAN ON switch on the limit control then the designer intended that the fan could be operated continuously.

On 2018-03-07 18:12:20.158130 by Ron MacDonell

heater fan motor runs on low..should it shut off on auto setting

On 2018-03-07 06:35:59.544537 by Jim

,
How long before the furnace starts to get damaged if the fan doesnt shut off.

On 2018-02-25 00:42:28.782623 by (mod) -

That's reasonable. Just check first for anything that you can recognize, obviously, by eye like a wire plugged into the wrong connector from the original setup

On 2018-02-24 23:43:17.009759 by Anonymous

,
Suggestions? Or should I just call a repairman?

On 2018-02-24 00:57:37.768523 by (mod) -

That sounds to me like a control board wiring error

On 2018-02-23 23:47:43.809713 by Michael

Just replaced fan in tempstar 10 outdoor AC. Last one was over heating. Now, when the compressor is on the fan stops. When the compressor stops, the fan turns on. So, what did I do wrong?? Gah!

On 2018-02-01 20:19:46.466211 by (mod) -

Larry

It's normal for a blower to stay on for a minute after the call for heat stops - to cool down the heat exchanger.
Beyond that a blower that stays on is doing so either because of a FAN ON switch setting (not your case) or because there's a problem: an overheated heat exchanger (maybe blocked air flow or dirty air filter) or a bad control board or limit switch.

IF the cycling on continues for many minutes or longer after the furnace has remained off then I suspect a bad control or relay.

OR for some furnace models such as the Norton D-series by Broan, a heat anticipator in your wall thermostat may be set incorrectly.

Note that not all thermostats even have a heat anticipator but some models do.

See HEAT ANTICIPATOR ADJUSTMENT https://inspectapedia.com/heat/Heat_Anticipator_Adustment.php

On 2018-02-01 19:37:23.883507 by Larry

Blower comes on for thirty seconds on my electric furnace them turns off for several minutes. I've turned the heat off at the thermostat but this doesn't stop the blower from cycling.

On 2018-01-16 16:00:05.566261 by (mod) -

Anne,

The cause is probably one of those listed in the article above,perhaps a bad fan limit switch.

On 2018-01-15 20:49:56.064537 by Anne

When the house reaches the desired temperature sometimes the fan keeps blowing even though the burners have stopped and the fan then blows cool air and does not stop.

I have to then turn the heat off and in a few minutes back on and then it runs properly by turning off. The fan is always set to auto.

On 2018-01-06 22:20:22.135893 by (mod) -

Chistina

Also see FURNACE BLOWS COLD AIR https://inspectapedia.com/heat/Furnace_Fan_Blows_Cold.php

and to rule out a problem at the thermostat see FAN WONT STOP - THERMOSTAT SWITCH https://inspectapedia.com/heat/Thermostat_Switch_Settings.php#FanStuckOn

On 2018-01-01 21:08:43.997913 by (mod) -

Christina,

Try looking through the steps in the article above and you'll see that there are several possible explanations for a fan that won't stop running. Just taking the batteries out of a thermostat might not even disable the thermostat.

On 2018-01-01 20:15:14.911556 by CHRISTINA

Even took the batteries out of the wall unit and it is still on and blowing out cold air

On 2018-01-01 20:13:44.115718 by Anonymous

Furnace will not turn off and keeps blowing out cold air

On 2017-12-30 00:55:41.568725 by (mod) -

Mike
Since on most forced warm air heating systems the blower does not come on until the plenum has warmed up, and since your system turns on immediately, I suspect that there is either an improperly set FAN ON switch that is forcing the fan into manual on position, or the limit switch is defective

On 2017-12-28 15:00:06.088681 by mike

Electric furnace blower comes on as soon as I turn on power at fuse box. If I take out fuses at furnace the elements will heat up. As soon as i put fuses back in fan starts and elements goes out. What could it be? Thanks

On 2017-12-27 02:45:22.455967 by (mod) -

That sounds strange indeed.

Try turning the power off switch OFF again, Leave it off for a minute, then turn it back on.

If that makes no difference, check the settings of the FAN switch at your thermostat as well as checking the diagnostic suggestions in the article above on this page.

On 2017-12-26 05:21:30.872224 by Angie

My husband changed the filter in the heater and hit the emergency power off then turned it back on now the fan won't stop running any suggestions

On 2017-12-16 23:23:05.643099 by (mod) -

Phil and Ben,

I agree that when the control board shows a fault light when the fan turns off that's diagnostic.

But could it not be a different fault - that is not the motor - that the control board is sensing, and in response to that fault it is turning off the motor?

I agree too that if the control board continually feeds power directly to the motor then there's a control problem. But if the board voltage is actually going first to a safety control like the fan limit switch then that's a different situation.

Do you have and did you check the wiring diagram for your unit?

When a blower fan won't stop I wouldn't expect a bad motor to be the direct cause, more likely it's a control or relay.

On 2017-12-16 22:49:35.492637 by BenC

@BenC,
I believe the problem is the motor. I have not confirmed this yet. But I have the Heat unplugged from motor control. When I trip the roll out or limit, blower shuts down. Meaning motor shuts down cause board goes into fault.

When time clears blower starts again. There is constant 120 from the board but blower should only start when heat or cool tells it to. With heat unplugged, the only 120 is thru the 120 and com. Which is normal. If it only shuts off when this is faulted and power is cut from these lines, and wires from fan control to blower ohm good, must be short internal on blower motor.

On 2017-12-10 17:09:17.594523 by Phil

Same problem here. Lenox constant blower no heat. no voltage to thermostat. Jumped limit and rollout limit.{they are in series} thermostat was powered and called for heat....for five min. then back to fan only. Do you think Circuitboard problem? 29 degrees outside on a Sunday

On 2017-12-07 04:51:09.084612 by BenC

@BenC,
Pertaining to my previous question from yesterday.

My furnace is an old Armstrong Series III 80 FYI
I now have replaced Limit switch. No Change.
Troubleshooting, I unplug Heat from Fan Control. Then Unplug either Roll Out or Limit. Blower stops, Induc fan turns on. Replace lead for Roll Out/Limit, Induc turns off and no blower. 2-3 min later

Blower fan starts.
If I do the above sequence and plug in Blue to Heat after shutdown from Roll Out/Limit, blower fan starts with everything off.

Thanks again.

On 2017-12-06 20:50:08.556516 by (mod) -

Anon - MIke:

Just so.
SOME (not all) fan limit switches include a white push-pull knob that forces the fan to run continuously - or leaves it on AUTO. That's what I suggest you look for first.

That switch and its operation as well as other causes for a fan that won't stop are listed in the diagnostic steps given in the article above, at
FURNACE FAN WONT STOP https://inspectapedia.com/heat/Furnace_Fan_Wont_Stop.php

On 2017-12-06 19:13:03.962084 by Anonymous

On that Lennox question I guess it's called the fan limit switch I think not sure just need to figure out before it gets to cold
Thank you

On 2017-12-06 19:02:57.992157 by Mike C

I have a Lennox furnace G10RQ3-110-2 that I just replaced and now the blower fun won't shut off I think that maybe I put the thermal switch upside down but not sure having a hard time finding information on a 1973 unit

On 2017-12-06 01:47:51.766626 by (mod) -

Set fan to AUTO,
Check the limit switch
Look for shorted control wires or relay

On 2017-12-05 18:58:00.237838 by BenC

I am having a strange issue that I can't seem to get to the bottom of. Hopefully someone can help!

Blower Fan is ON and will not turn off.

Heat - OFF, Fan - AUTO = Fan stays ON

Disconnect ALL thermostat wires from Fan Control panel = Fan Stays ON

Replaced Fan Control Panel with New = Fan Stays ON

Wacked Blower Motor with BFH = Fan Stays ON

Thank you in advance

On 2017-11-30 23:23:59.383601 by (mod) -

Interesting problem, I'm not sure what's going on. The first thing I would check is whether or not the thermostat is calling for heat. When your fan is running continuously if you set the thermostat all the way down to his lowest temperature then the fan might run for another minute or two but then it should stop.

If that happens then the problem is probably not with your fan but rather that your building is losing Heat and the heating system is working like mad trying to keep you warm.

On 2017-11-30 18:42:50.124413 by Ryan

Hi, I'm having the problem of the blower running continuously, but it will turn of sometimes. It runs continuously about 90% of the time but occasionally after a heating cycle the blower will shut off like normal. Any suggestions?

On 2017-11-26 23:47:26.740068 by (mod) -

Anon

If testing confirms the thermostat wires are shorted together, then you either find and repair the short or run new thermostat wires

On 2017-11-11 19:25:39.885428 by Anonymous

If they were accidentally shorted together what do I need to do? I verified wiring and appears to be correct. I do know that we relocated the thermostat and had to add some thermostat wire to existing in order to reach the spot we wanted.

On 2017-11-11 by (mod) - fan continually runs and heat is warm then cool after upgrading thermostat

CJ

If those heater problems have happened since the installation of the new thermostat I suspect
- mis-wiring
or
- thermostat wires accidentally shorted together

Saul:

Reasons that a blower won't turn off when the thermostat-set-temperature has been reached are given in the article above starting at https://inspectapedia.com/heat/Furnace_Fan_Wont_Stop.php

On 2017-11-11 by CJ

Recently upgraded thermostat to digital. Now fan continually runs and heat is warm then turns cool
And can won't stop blowing. What did I do wrong?

On 2017-11-10 by Saul

Why blower won't turn off when hot tempetur is reach

On 2017-10-31 by Anonymous

Can’t find limit switch

On 2017-10-28 by james

my furnace fan wont stop running if i tap the side of furnace it some times will shut off what can i do

On 2017-10-04 by paul

silver dial on fan control switch sticks. Blower doesn't shut off on its own but if I tap silver dial it pops and stops blower. Can it be rusty or dirty behind silver dial. can i do anything to stop it from sticking.

On 2017-10-02 by ken

oil furnace will come on fan will come on bu it will keep burning and not shut off even when desired temperature is reached

On 2017-09-26 by (mod) -

Tim

Check first that there is not a manual fan ON switch set at the thermostat or at a fan limit switch if your fan also is incorporated in a heater (furnace). Did you try going through the diagnostics in the article above?

If there is no switch problem it's possible that a control board for the fan or blower assembly was damaged.

On 2017-09-26 by tim p.

during power outage of hurricane irma i had my portable ginnie feeding power to the house.the havac system pulled to heavy of a load so threw the braker on it.

after power restored the a/c unit works fine but squrill cage will not shut off.replaced thermostat still runs continousley.

On 2017-08-20 by (mod) -

C

This doesn't sound right to me. I'm not aware of any situation in which a kitchen exhaust vent fan would have the slightest thing to do with the central heating system furnace.

However, if during work on the vent fan you drove a nail or screw that shorted the furnace thermostat wires together, that'd keep it running.

See FAN WONT STOP - LIMIT SWITCH -https://inspectapedia.com/heat/Furnace_Fan_Wont_Stop.php for more diagnostic help

On 2017-08-18 by C

Recently I replaced my hoodfan in my kitchen. It is tied to the furnace but now the furnace won't turn off even though I have the thermostat switched to off

On 2017-08-14 by Tony

Fan blower motor running none stop for the past week. The only way to stop it is pull out main fuse or unplug the blow fan wire. please help and advise.

On 2017-08-09 by Jamie

I have AC blower that will not stop . The thermostat I replaced with my spare ( digital ) . Still some issue . Have the unit shut down to see if the limit switch is able to reset . If not where can I get a part number for the limit switch ?

On 2017-07-06 by (mod) -

The system isn't cooling. Use the on-page search box at the top or bottom of this page to find our article on LOST COOLING to see a diagnostic list of causes to investigate.

On 2017-07-05 by Anonymous

I have my thermostat set at 76 degrees but it will not go less than 79. Unless it reaches 76 degrees,the blower won't shut off. What can it be?

On 2017-06-25 by Nate

Replaced thermostat. Replaced fan switch/limiter. All brand new. The blower will not stop running unless I flip the circuit breaker switch. HELP!

Literally, the moment I close the circuit breaker switch for the indoor furnace. the blower immediately starts and runs FOREVER. The ONLY way to stop it is via the circuit breaker.

Everything else works fine, such as the outdoor compressor. I removed the green wire from the G terminal at the furnace, yet the blower keeps running! This is a 15+ year-old system. Is there anything else I can check? I cannot afford an entirely new system at this point.

On 2017-06-22 by michael

Well with my indoor vertical unit the blower fan turns itself on and off and regardless of what temp it's set at. I'll come home from work and it's been turned off all day, I turn it on to cool set at 76 degrees and the system turns on, outside unit runs perfectly but after a few minutes the inside blower turns itself off while the outside unit keeps running.

The blower continues to turn itself on and off for awhile even if I switch the thermostat off, what's going on with this thing? I really wanna fix this myself so Any help/advice is appreciated ! Thanks

On 2017-06-01 by (mod) - look for a short in thermostat wires or a shorted control board

Ed,

If you have been through the diagnostic suggestions in this article, and don't see a fix for your system, then it sounds to me as if there's a control failure or shorted wires.

On 2017-06-01 by Ed

Blower fan is on cannot shut off unit and can't turn system on!

On 2017-04-28 by (mod) - Thank you so much for posting this article!

Thanks for the feedback Sarah; we work hard to provide researched unbiased data, so I'm really happy when a reader finds that effort useful.

Daniel

On 2017-04-27 by Sarah

Thank you so much for posting this article! I was able to troubleshoot and fix without calling a repairman.

On 2017-03-21 by (mod) - fan stops when disconnect the thermostat

Marci

If the fan stops when you disconnect the thermostat but otherwise runs constantly regardless of any thermostat switch settings, I suspect that the thermostat is damaged OR there are shorted or mis-connected thermostat wires.

On 2017-03-21 by Marci

Now what do I do for that

The fan on my heating and cooling system won't shut off unless I take the thermostat off I even tried shutting the whole thing off from thermostat

On 2017-03-16 by (mod) - how & where to find the fan limit control switch

Hershel

Click on this article: FAN LIMIT SWITCH and you'll see photos of the control that give its typical location.

Because the limit control switch has to sense the air temperature inside the furnace it will always be mounted on the furnace, typically on or close to the supply air plenum, thus on the upper are of most furnaces (some oil furnaces locate the control lower in the unit).

The switch will usually be under or behind the furnace cover that's removed to give access to the furnace burner and controls,

or

On some furnaces you'll see the fan limit switch mounted on a supply air plenum (chamber) above the burner and heat exchanger section - that is, at the start of duct work that carries warm air into the building occupied space.

On 2017-03-15 by Hershel Thomas

My blower motor will not stop running unless I turn thermostat down about 10 degrees below temp reading. Where is motor limit switch located? Could it be a faulty thermostat? Thanks. H. Thomas

On 2017-03-15 by (mod) - The furnace starts i/s cycle but does not start.

No, if the fan runs but the burner doesn't ignite then the problem is fuel, burner, or control.

On 2017-03-15 00:51:51.365364 by Lienhart

The furnace starts i/s cycle but does not start. The fan is on all the time. Is it an issue with my limit switches for my fan

On 2017-03-06 01:48:29.688328 by (mod) - My heater blower is constantly running but no air is coming thru vents

That sounds like disconnected air ducts. A blocked or dirty filter might slow air but wouldn't normally stop it completely.

Start by checking in the blower compartment - that the fan is working.
Then follow the ductwork

On 2017-03-06 01:40:12.777218 by Cy

My heater blower is constantly running but no air is coming thru vents

On 2017-02-21 by (mod) -furnace hets up blower runs after heat is gone blows cold

Sounds like a loose wire or a failed limit control switch.

On 2017-02-21 by paul

furnace hets up blower runs after heat is gone blows cold i gently tap manual/auto switch then it shuts off

On 2017-02-06 by ecurry

Why does my unit continually run and blow out cold air even after I shut it off at the upstairs control?

On 2017-02-01 by (mod) - fan on my hvac unit won't shut off, on backup heat

If your system is running on backup heat I suspect the backup heater is not working.

Someone asked:

My indoor fan on my hvac unit won't shut off. My ac works but my heater doesn't

On 2017-01-19 by ryan

hi , i have a goodman PG036100 unit so was working fin until last 2 weeks ago and start having some issues

when i put thermostat on heat on the AC turn on and when i put it on AC the heat works so i leave it on AC on that way i get some heat so now the heat keeps working even the thermostat is off , i thought from the thermostat so i changed it but still the same problem

On 2017-01-18 by Avril

I have to turn my heater off by the curcuit breaker in my mobile home. The thermostat is set on auto and off but it keeps on running. Can you please help me?

...

...

Continue reading at FURNACE FAN WONT STOP or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see FURNACE FAN WONT STOP FAQs-3 - more-recent questions and answers on blower fans and air handlers that just won't stop running

Or see these

Recommended Articles

• AIR HANDLER / BLOWER UNITS - home
• BLOWER FAN CONTINUOUS OPERATION
• BLOWER FAN OPERATION & TESTING - home
• BLOWER FAN WONT STOP - LIMIT SWITCH
• BLOWER FAN WONT STOP - THERMOSTAT SWITCH

Suggested citation for this web page

FURNACE FAN WONT STOP FAQs-2 at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

Or see this

INDEX to RELATED ARTICLES: ARTICLE INDEX to HEATING FURNACES

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