Furnace Exhaust Fan Runs Continuously

If that fan switch is set to man manual or on it will force the blower to run continuously.

Furnace exhaust fan runs continuously.

Set incorrectly to manual or faulty and needs to be repaired replaced. 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.

Remove the panel from your furnace and locate your fan limit switch. 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. The electronic limit switches are disc shaped and mounted on the exhaust pipe at the furnace. This switch is located just under the furnace hood.

Check the small white button on the switch. Pull the white button out to reset your fan limit switch to auto. The fan auto off or fan on off switch on the room thermostat should be checked. 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.

Locate your fan limit switch and check to see if the white knob see pic below is pressed in. At the room thermostat. The fan does have a pressure switch to prove to the micro that the fan is running for ignition to take place. A malfunction in the microcontroller pic on the circuit board or a short could cause the fan to run continuosly.

Check to make sure the limit and rollouts are all closed. Pros to running fan on air conditioner continuously. If so your switch is. Does the furnace work as normal aprt from the continuously running fan.

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. Follow the steps below to check the settings of your fan limit switch. It does not control the fan directly. The fan limit switch may include a switch that manually.