3 Reasons A Furnace Blower Fan Won't Shut Off

When your furnace fan doesn't shut off, you'll want to figure out why so the fan doesn't run up your power bill and so it's easier to control the temperature in your home. First, make sure the thermostat is set properly and that you don't have the fan set to run continuously. If the thermostat appears to be set correctly, call a furnace repair company to figure out the problem and make repairs. Here are three things that might be wrong.

1. The Thermostat Is Bad

The thermostat might be set properly, but if the wiring is bad, or the thermostat itself is bad, your furnace can behave erratically. A repair technician can test the thermostat and wiring to see if either needs to be replaced. Unless a thermostat can be cleaned or have the wiring replaced to make it work again, it will probably need to be replaced.

2. The Limit Switch Is Stuck

The limit switch turns the fan on and off in response to the thermostat turning the heat on and off. If the switch gets stuck or fails, it won't turn the fan off and it will keep blowing. The limit switch is also a safety mechanism that shuts the furnace down if the temperature gets too hot in the furnace because the fan fails.

If the switch is bad, it needs to be replaced. The repair technician can do this by removing the old switch and putting in a new one. But first, they may check the wiring to make sure loose or bad wiring isn't the problem.

3. The Control Board Is Bad

Your furnace has a control board that operates all the electronic parts in your furnace, including safety mechanisms. When the control board fails, your furnace may start doing odd things, and your furnace may not work at all.

A common problem with the control board is loose wiring. Wiring gets loose inside your furnace because of the vibrations from the fan running and your furnace kicking on and off. Loose wiring can short out and cause even more problems. If the wiring to the control board is bad, the furnace repair technician can replace the wiring and solve the problem.

A control board can also fail due to a power surge, soldering failure, or failure of the electronic parts it contains. It might be possible to repair a furnace control board, but if not, the technician will need to replace it since the circuit board controls so many aspects of how your furnace works including shutting down the fan after a heating cycle.