Honeywell Home Stuck Fan Relay or Miswired G Circuit

The thermostat fan runs continuously even when set to Auto and there is no call for heat/cool.

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 the furnace board, G wire shorted to R, Fan set to circulate mode in the thermostat, Incorrect wiring at the thermostat

Safety: Turn off power to the furnace/air handler before inspecting wiring.

Check fan setting: Ensure the thermostat fan mode is set to Auto, not On or Circulate.
Inspect G wiring: At the thermostat and furnace board, verify that the G wire is not touching R or any other terminal.
Test relay (advanced): With power off, remove the G wire from the furnace board. Restore power; if the fan still runs, the fan relay is stuck closed and the control board may need replacement.
Replace control board: If the fan relay is confirmed stuck, replace the furnace control board or fan relay module.

Hard 4/5

Furnace Control Board

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