Furnace Exhaust Fan Runs Continuously

At the room thermostat.

Furnace exhaust fan runs continuously.

This switch is located just under the furnace hood. Does the furnace work as normal aprt from the continuously running fan. 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.

The electronic limit switches are disc shaped and mounted on the exhaust pipe at the furnace. Pull the white button out to reset your fan limit switch to auto. Less frequent starts and stops of the fan can reduce the stress from startup and potentially help extend it s lifespan. The fan auto off or fan on off switch on the room thermostat should be checked.

Remove the panel from your furnace and locate your fan limit switch. If that fan switch is set to man manual or on it will force the blower to run continuously. A malfunction in the microcontroller pic on the circuit board or a short could cause the fan to run continuosly. 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 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. 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. But if the furnace fan runs continuously regardless of whether the furnace is heating or not your furnace fan limit switch is either. One of the limit switches is locked in the open position so the fan runs continuously.

At the furnace or air conditioner air handler or blower unit. Check the small white button on the switch. If so your switch is. This will cause the fan to automatically turn on.

Set incorrectly to manual or faulty and needs to be repaired replaced. The fan limit switch may include a switch that manually. Check to make sure the limit and rollouts are all closed. Follow the steps below to check the settings of your fan limit switch.