Why Does My Furnace Fan Keep Running? A Texas Technician Answers


One thing you should realize right from the get-go is that you’re not the only one to experience this problem. It’s actually more common than most people think. But, before you pick up the phone or schedule anything, take a look at your thermostat/furnace first.

There are a few possibilities that could be the root cause of the problem. Some of which can be fixed yourself and some of which may need a pro’s touch.

Some situations that could cause a furnace fan to constantly run include:

  • Using the wrong thermostat setting
  • The fan limit switch is on the wrong mode
  • Faulty equipment

In what follows, we’ll go through each one together and how you (or we) can go about fixing them.

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Using the wrong thermostat setting

We’ll start with the more obvious/simple fix. First, be sure that your fan setting is set to AUTO instead of ON.

If your fan is set to ON, that means you have it so the fan runs 24/7, whereas the AUTO setting only runs the fan during heating cycles. This should solve your problem. If not, you’ll have to take it one step further.

Once the thermostat is set to AUTO, adjust the temperature so that it’s lower than the temperature of the room. This will trigger the furnace to shut down and stop the thermostat from calling for additional heat.

Thermostat to AUTO not ON

Now, just wait for about 3-4 minutes and see if the furnace fan shuts off.

If the fan does shut off after you've adjusted the thermostat, this could just mean that your furnace fan is running continuously because the furnace itself is heating your home constantly, (which might or might not indicate a problem).

Another factor to consider is if it's a really cold day, your furnace might just need to run non-stop to keep your home warm. Or it could mean that you’ve set your temperature too high, making the furnace (and likewise, the fan) run constantly.

Note: If you're concerned with how long your furnace is running, you should consider having a tech inspect the system to determine if there's a real underlying problem or not.

Still no luck? Okay, let’s dig a little deeper.

The fan limit switch is on the wrong mode

For those not too familiar with it, the fan limit switch on your furnace controls when the blower fan is turned on or off. It serves as a safety tool as well, as it will automatically turn off the burner if the temperature is getting too high at the furnace.

Now, if the furnace fan won’t stop running, it may be that either your limit switch has been set to manual override, or the switch itself is faulty and needs to be replaced.

Your fan limit switch can be found right under the furnace hood. Have a close look at it. You should see a little white button/knob, this is your fan limit switch.

If that white button appears to be pushed in, the switch has been set to manual override, which means the fan will run constantly. By simply pulling the white button out, you’ll reset the switch to AUTO mode.

Faulty equipment

If the fan limit switch/button is already pulled out, chances are that you have a bad switch or a shorted thermostat wire. Both scenarios need to be addressed immediately and will require a professional to repair. We can help you there!

Need help from one of our Texas Techs? There’s no job too big.

We’ll troubleshoot whatever is causing your furnace fan to constantly run, and we’ll give you upfront estimates on how much it will cost to fix. No games or gimmicks. Just reliable.

To learn more about what to expect when you hire us, visit our furnace repair page. Or just give us a call at 512-580-8837.

Schedule an appointment today