Fraser-Johnston Continuous Fan Operation

Furnace blower runs continuously even when thermostat is not calling for heat.

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

Thermostat fan set to ON instead of AUTO, Stuck blower relay on IFC board, High limit switch open, Fan‑only jumper installed on control board

Safety first: Turn off power before opening the furnace cabinet.

Check thermostat fan setting: Ensure the fan mode is set to AUTO, not ON.
Observe control board LED: If a limit fault code is present, the blower may be running to cool the furnace. Address the underlying limit issue (filter, airflow).
Inspect blower relay: If no fault codes and fan still runs, the blower relay on the IFC may be stuck closed. This typically requires control board replacement.

Medium 3/5

Integrated Furnace Control Board

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