What This Error Means

The furnace control allowed the available ignition attempts but did not verify an established burner flame. The control stops the ignition sequence and enters a lockout or timed restart condition.

Symptoms You May Notice

No heat; inducer may start; igniter may glow; burners may not light; burners may light briefly and shut off; repeated ignition attempts; fault remains in alarm history.

Common Causes

Dirty or poorly positioned flame sensor; damaged hot-surface igniter; gas supply interruption; closed manual gas valve; gas valve not opening; blocked intake or exhaust; pressure-switch problem; loose ignition wiring; defective furnace control.

Safe Troubleshooting Steps

1. Turn off furnace power before opening panels. 2. Confirm the manual gas shutoff is open and other gas appliances have fuel. 3. Inspect intake and exhaust terminations for blockage. 4. Inspect the igniter for cracks or an open circuit. 5. Inspect and clean the flame sensor only with an appropriate nonabrasive method. 6. Observe whether the gas valve receives the specified control voltage during ignition. 7. Verify flame-sense current and grounding according to the service documentation. 8. Have a qualified technician test gas pressure, valve operation and the integrated furnace control.

Parts Commonly Involved

Hot-surface igniter; flame sensor; gas valve; pressure switch; inducer assembly; integrated furnace control; wiring and grounding; intake and exhaust venting.

When to Call a Technician

Yes, unless the issue is a clearly visible vent obstruction or closed external gas shutoff that can be addressed safely.

Safety Notice

Do not repeatedly reset the furnace or bypass ignition, gas-valve or pressure-switch safeties. If gas is smelled, leave the building and contact the gas utility or emergency services.

Manufacturer Documentation