Thermostat Fan Won't Turn Off? How to Stop It Running

The Short Answer

Nine times out of ten the fan is running because the thermostat told it to: the fan is set to On, a fan timer or hold is active, or a fan schedule or minimum runtime runs it every hour. All of these keep working even when the system is set to Off, which is why a fan that keeps running after the system is switched off is so common.

If you have ruled all of those out and the fan still runs, the problem is in the equipment or wiring, not the settings (see the last section).

Auto vs On: Check This First

Honeywell’s explanation applies to almost every thermostat: on Auto, “the fan will not blow air unless there is a call from the system”; on On, it runs continuously whether or not heating or cooling is running. Some Honeywell models add Circulate, which runs the fan about 35% of the time, roughly 20 minutes each hour. Set it to Auto if you want the fan to run only with heating or cooling.

On a Nest Thermostat

• Fan timer: starting the fan manually runs it for the time you chose (15, 30, 45 or 60 minutes). Google says to select Stop in the fan menu to end it early.
• Fan schedule: a daily schedule turns the fan on automatically at set times. Edit or turn it off in the fan menu.
• Fan duration: sets how many minutes per hour the fan runs within the schedule.

The catch Google points out: when the fan is turned on manually, it can keep running even when the thermostat is set to Off. Turn the fan off in the fan menu, not just the system.

On an ecobee

• Fan minimum runtime: runs the fan a set number of minutes every hour, in any system mode. ecobee’s path: Main Menu → General → System → Fan on Premium and Enhanced; Main Menu → Fan Mode → Auto on Lite and Essential. Set it to 0 to stop it.
• Fan hold / fan timer: runs the fan for a set time or indefinitely. ecobee notes holds stay active in Off mode but you cannot see them there: switch the system mode to anything but Off to check and cancel.
• Fan in Comfort Settings: a Comfort Setting (Home, Away, Sleep) can have its fan set to On, which runs it for as long as that setting is active in Heat, Cool, Auto or Aux mode. Set it to Auto in each Comfort Setting.

Details and menu paths are in ecobee’s fan settings article.

On a Honeywell Thermostat

Set the fan to Auto (not On or Circulate), and check whether a fan schedule is set in the app or on the thermostat. On models with Circulate, remember it deliberately runs the fan part of every hour.

If It Still Won’t Stop: Equipment or Wiring

Test it: set the thermostat to Off and the fan to Auto, cancel any timers and holds, and wait a few minutes. If the fan still runs:

• Pull the thermostat off its wall plate. If the fan stops, the thermostat or its wiring (the G wire) is calling for it; recheck the settings or the wiring.
• If the fan keeps running with the thermostat removed, the call is coming from the equipment: a stuck fan relay on the control board, a limit switch keeping the blower on to cool an overheating furnace, or a control board fault.
• An overheating furnace is often a clogged filter: replace it. If the fan still will not stop, turn the system off at the furnace switch and call an HVAC technician.

Frequently Asked Questions

Why won’t my thermostat fan turn off?

Usually the fan is set to On instead of Auto, or a fan timer, hold, schedule or minimum runtime is active; these can keep running even when the system is off. If none are set and the fan runs with the thermostat removed from the wall, it is an equipment fault.

Should my thermostat fan be on Auto or On?

Auto runs the fan only when heating or cooling is running. On runs it continuously, which moves air but uses more electricity.

Why does my fan run with the thermostat off?

A manual fan timer on a Nest, or a fan hold or minimum runtime on an ecobee, keeps running in Off mode. If none is set, the furnace or air handler is running the blower on its own; call a technician.

Can a dirty filter make the fan run constantly?

It can make the furnace overheat, and the safety limit keeps the blower running to cool it down. Replace the filter; if the fan still will not stop, call a technician.

Related Guides

• Thermostat clicks but nothing happens — the opposite problem
• AC short cycling — turning on and off too often
• Smart thermostat troubleshooting — every fix guide by symptom

Sources

• Google Nest Help: Fan control with a Nest thermostat
• ecobee Support: Fan settings on the ecobee thermostat
• Honeywell Home: Thermostat fan Auto/On guide