Gibson Fan-Only Cycling / Control Logic Fault

Furnace blower starts and stops repeatedly without burner ignition

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

Stuck fan relay on Gibson control board, Miswired thermostat fan circuit, Faulty fan timer, Intermittent limit switch causing fan purge cycles

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

Steps to check:

Thermostat fan mode: Confirm the thermostat is not set to a fan-circulation program.
Check G wiring: Temporarily remove the G wire from the control board. If the blower cycling stops, the thermostat or wiring is causing the issue.
Control board: If blower continues to cycle with G removed, the fan relay or timer on the board may be failing and the board should be replaced.

Medium 3/5

Fan Control Board

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