Furnace Exhaust Fan Runs Continuously

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

Furnace exhaust fan runs continuously. Pros to running fan on air conditioner continuously. Locate your fan limit switch and check to see if the white knob see pic below is pressed in. Does the furnace work as normal aprt from the continuously running fan. If so your switch is.

Pull the white button out to reset your fan limit switch to auto. This switch is located just under the furnace hood. A malfunction in the microcontroller pic on the circuit board or a short could cause the fan to run continuosly. Remove the panel from your furnace and locate your fan limit switch.

Check the small white button on the switch. At the furnace or air conditioner air handler or blower unit. One of the limit switches is locked in the open position so the fan runs continuously. This will cause the fan to automatically turn on.

The high limit in the heat exchanger if tripped will initiate lock out and will auto reset after time or killing power as described however the indoor blower will run continuously ass described by another expert and his york unit this is by design and for safety to get the ignition module to reset still requires killing power this is so we do not miss a cracked heat exchanger or similar dangerous condition. The fan auto off or fan on off switch on the room thermostat should be checked. Less frequent starts and stops of the fan can reduce the stress from startup and potentially help extend it s lifespan. Follow the steps below to check the settings of your fan limit switch.

If that fan switch is set to man manual or on it will force the blower to run continuously. It does not control the fan directly. Set incorrectly to manual or faulty and needs to be repaired replaced. If your furnace goes off on high limit or if one of the rollout switches are open then the furnace fan will run all the time because the furnace control board is telling the furnace that the furnace has over heated and the fan runs to cool the furnace down.

The electronic limit switches are disc shaped and mounted on the exhaust pipe at the furnace. Keeping the fan on creates a more even distribution of heating and cooling circulating the air if you have cold or hot spots in your house like a bedroom above a garage. If the bad limit switch was locked in the closed position the exhaust fan would not turn on when was a call for heat and no signal to the control board preventing the furnace to turn on. At the room thermostat.