Honeywell Thermostat Fan Won’t Turn Off? [8 Reasons & Solutions]

Honeywell thermostats are among the most trusted brands of thermostats, partly because the makers have been in the market for quite a long time and know how to create just what consumers love. However, you may experience a glitch that won’t turn off the fan at one point or another, and you may be looking for a solution.

If a Honeywell thermostat fan doesn’t turn off when your system goes off cycle, that could be a sign of any of the following:

• The thermostat has incorrect settings,
• You have a stuck fan relay
• The fan limit switch is wrongly set
• You have a malfunctioning limit switch
• Bad thermostat wiring
• An inefficient cooling/heating system
• Malfunctioning or defective board
• A defective thermostat

Possible Reasons & Fixes for a Honeywell Thermostat Fan That Won’t Turn Off

1)      Incorrect Thermostat Settings

One of the first things you want to do when you notice that your thermostat is not turning off is to check your thermostat settings. The thermostat could be set to on and be the reason your fan could be running nonstop.

You might not have adjusted your thermostat, but others in your household might have.

Before you go far, inspect the thermostat for a FAN ON or Fan Auto function.

A typical thermostat has 2 or 3 fan selection key: on, auto, and or/ circ.

The system fan will run on the auto setting when the thermostat calls for heating or cooling. Under this setting, the fan will not run when the system is not on heat or cool.

On setting: The fan will always run regardless of whether or not the system is cooling or heating.

The circ position, if available, runs 35% of the time. This setting is mainly used where is low seasonality demand, such as in fall or spring.

The fix.

Double-check your thermostat once more and set it to auto if it’s on. Test if it can turn off now. If it keeps running, there could be another issue causing this.

2)  Stuck fan relay

Another thing that could prevent your thermostat fan from turning off is a furnace fan limit control stuck in the closed position.

If you have taken the thermostat off the wall and disconnected the wires, you can try removing the green wire from the thermostat. If the fan keeps running, it is a problem with a stuck fan relay.

Circuit relays open and close circuits to components of your air conditioner or furnace, such as fans and compressors.  

Relays can become stuck in either open or closed positions for several reasons. If a fan relay is stuck in the closed position, it will always supply the electricity to your fan, making it run throughout.

So, even if you turn off your thermostat, you’ll notice that your fan will continue running.

3)  Fan limit switch set to manual override

When the limit switch is set to manual override or when it is pressed, it simply means that it will run your fan continuously and will ignore any instructions from your thermostat to stop it.

The limit switch is located inside the furnace cover. It will typically have a white button at the lower left corner. When the button is pressed, it’s in the manual override mode and will cause the fan to run continuously. Ensure that the button is not pressed for the fan to run on automatic.

4)  Defective limit switch

The fan’s limit switch is responsible for turning the fan on and off at the appropriate times. When there is a call for heat from the thermostat, the limit switch will turn on the fan several minutes later, and when there is a call for cooling, it will function likewise.

However, when the limit switch is defective, it will not respond to your Honeywell thermostat’s call to stop running. That could be the reason the fan is running nonstop.

The fix

If the switch is defective, you can try resetting it; otherwise, you’ll have to call a professional to come and fix it.

5)  Bad thermostat wiring

Bad thermostat wiring could be the culprit. The g wire controls the fan’s relay, but when this wire is shorted with another wire, it could energize your fan, and that can make it run continuously.

The fix

Check the thermostat wiring and, if possible, look into the user manual about the correct thermostat wiring.

Sometimes your system could just be operating normally. Most Honeywell thermostats use a 1-degree(f) differential, so they will continue heating until +0.4 degrees of the setpoint and kick in once it drops to -0.4 degrees of the setpoint.

 That usually happens when cold out and needs to remain on to maintain the temperature within the differential band.

6)  System inefficiencies

Another reason that could cause your Honeywell thermostat to run without turning off is dirty filters.

When you have dirty filters, your thermostat fan will run continuously to try and reach the set temperatures. The inefficiency of the system could be due to the following:

• Clogged or restrictive air filters
• Dirty or frozen evaporator coils
• Dirty or blocked condensers
• Or low refrigerant

7)  Malfunctioning Control Board

If everything above is not the case, you might have a defective control board. A control board is usually found in the air handler. Its primary responsibility is to receive instructions from the thermostat and relay them to other parts of your air conditioner or heat pumps, such as the fan or gas valve.

When this part of your system malfunctions, it can bring about all sorts of problems.

The fix

The best thing to do if you believe that you have a defective control board is to call an HVAC technician. He/she can use special tools to help troubleshoot your system and possibly fix it.

8)  Defective thermostat

Other times, It’s just the thermostat that has served its purpose and needs a replacement. That’s especially true if your home’s thermostat has worked for quite a long time. 

In that case, the final solution is to replace your defective thermostat with one that is not faulty.

Tim David

HVAC tech with over 30 years of experience. Retired and doing repair work on the side around Madison County, AL.