What This Error Means

The furnace control senses a flame signal at a time when no burner flame should be present. The furnace stops normal operation because this may indicate a gas-valve, flame-sensor, wiring or control fault.

Symptoms You May Notice

Furnace locks out before ignition; inducer or blower may run as a safety response; fault appears without a normal burner cycle; possible abnormal gas-valve behavior.

Common Causes

Gas valve leaking or stuck open; gas-valve relay stuck; flame-sensor wire shorted to voltage; contaminated sensor creating a false signal; moisture; defective integrated furnace control.

Safe Troubleshooting Steps

1. Turn off furnace power and close the manual gas shutoff. 2. Do not repeatedly reset the furnace. 3. A qualified technician should verify that no flame or gas flow is present with the valve de-energized. 4. Inspect flame-sensor wiring for shorts or moisture. 5. Test the gas valve and furnace-control relay. 6. Replace defective components and perform leak and combustion testing before returning the furnace to service.

Parts Commonly Involved

Gas valve; flame sensor and wire; integrated furnace control; gas-valve relay; burners.

When to Call a Technician

Yes, immediately.

Safety Notice

Shut off furnace power and gas. A false or unexpected flame signal can indicate unintended gas flow or a failed safety-control circuit.

Manufacturer Documentation