Day & Night Fan Off-Delay / Stuck Fan Relay

Furnace blower continues to run for a very long time after burners shut off, blowing cool air.

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

Possible Causes

Incorrect fan off-delay setting, control board fan relay stuck closed, high-limit switch cooling cycle extended due to overheating

Safety first: Turn off power before accessing the control board.

Thermostat fan mode: Confirm the thermostat fan is set to AUTO, not ON.
Observe cycle: Time how long the blower runs after burner shutdown. Normal off-delay is typically 60–120 seconds.
Check for overheating: If the blower runs much longer and the furnace is very hot, address airflow issues (filter, registers) first.

If the blower never shuts off, the fan relay on the control board may be stuck and the board will need replacement.

Medium 3/5

Integrated Furnace Control Board

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