Philco Stuck Fan Relay or Fan Switch Setting

Furnace fan runs continuously even when thermostat is set to AUTO and no heat call is present.

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Safety Warning

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.

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Possible Causes

Thermostat fan set to ON, Stuck fan relay on control board, Short between G and R thermostat wires, Faulty fan limit control (older models)

How to Fix / Troubleshooting

Safety first: Turn off power before inspecting wiring or the control board.

Homeowner checks:

  • 1. Check thermostat fan setting: Ensure it is set to AUTO, not ON.
  • 2. Inspect thermostat wiring: At the furnace control board, verify G and R wires are not touching or shorted.
  • 3. Power cycle furnace: Turn power off for 5 minutes, then back on. If the fan starts immediately with no call, the relay may be stuck.

When to call a professional: A technician should test the fan relay on the Philco control board and replace the board if the relay is welded closed.

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Repair Difficulty

Medium 3/5

Required Part

Ignition Control Board
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