Furnace Exhaust Fan Runs Continuously

Check the small white button on the switch.

Furnace exhaust fan runs continuously.

A malfunction in the microcontroller pic on the circuit board or a short could cause the fan to run continuosly. Locate your fan limit switch and check to see if the white knob see pic below is pressed in. The fan auto off or fan on off switch on the room thermostat should be checked. 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.

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. Pros to running fan on air conditioner continuously. Set incorrectly to manual or faulty and needs to be repaired replaced. This switch is located just under the furnace hood.

It does not control the fan directly. If that fan switch is set to man manual or on it will force the blower to run continuously. Pull the white button out to reset your fan limit switch to auto. 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 limit switch may include a switch that manually. 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. If so your switch is.

Less frequent starts and stops of the fan can reduce the stress from startup and potentially help extend it s lifespan. This will cause the fan to automatically turn on. The fan does have a pressure switch to prove to the micro that the fan is running for ignition to take place. Check to make sure the limit and rollouts are all closed.

Does the furnace work as normal aprt from the continuously running fan. At the room thermostat. At the furnace or air conditioner air handler or blower unit. But if the furnace fan runs continuously regardless of whether the furnace is heating or not your furnace fan limit switch is either.