Why Does My Furnace Fan Keep Running?

Have a furnace fan that runs continuously?

First, try this: Make sure your thermostat fan setting is on AUTO not ON. Then, turn the thermostat to a temperature that’s lower than the current room temperature and wait 3 to 4 minutes.

Furnace fan still running? Well, that’s not normal. If your furnace fan won’t turn off, you most likely have one of these 3 problems:

• Your furnace fan limit switch is set to “manual override”
• The fan limit switch is faulty and needs to be replaced
• There’s a problem in your thermostat wiring

Unfortunately, you’ll need a professional to fix those last 2 problems. But before you call in a pro, check to see if your fan limit switch is set correctly. We’ll show you how to do that in this article.

Need a professional ASAP? Just contact us and we can get your furnace fan running normally in no time.

Step 1: Locate your fan limit switch

Your fan limit switch is located inside the furnace panel cover, usually near the upper right corner.

The fan limit switch is responsible for turning the blower on and off at the appropriate times. So, when the switch is working correctly, your furnace fan should turn on several minutes after thermostat calls for heat and turn off several minutes after the heat cycle ends.

But if the furnace fan runs continuously, regardless of whether the furnace is heating or not, your furnace fan limit switch is either:

• Set incorrectly to Manual or
• Faulty and needs to be repaired/replaced

Now that you’ve located your fan limit switch, let’s look at how you can determine whether it’s set correctly or not.

Step 2: Make sure the white button is NOT pressed in

Your fan limit switch will have a small white button on the lower left corner. That button tells the switch whether to operate manually (run the fan all the time) or automatically (run the fan only during heating cycles).

If the button is pressed in, the switch is set to Manual and is forcing the fan to run continuously. You’ll need to reset it to AUTO to allow for proper fan operation (see pic below for instructions).

Step 3: Call a professional if the fan is still running

If your fan limit switch is set to AUTO but the fan continues to run without ever stopping, you’ll need to call a professional.

Two problems that could cause your fan to run without stopping include:

• A bad fan limit switch that needs to be replaced
• Bad thermostat wiring

Need help from an expert furnace repair tech?

If you’re still having trouble with a furnace fan that won’t shut off, we’re here to help. Coolray serves the Atlanta, Nashville and Birmingham, AL metro areas and more with professional heating & air conditioning services.

Just contact us and we’ll send out an experienced tech as soon as possible.

Related reading:

• 3 Common Furnace Problems in Atlanta
• Furnace Troubleshooting: 4 Quick Fixes Before Calling a Pro