Furnace will not start; LED flashes 10 times repeatedly.

Safety: Turn off power and gas before removing burners or flame sensor.

• Clean flame sensor: Remove the flame sensor and gently polish the rod with fine steel wool. Wipe with a clean dry cloth and reinstall.
• Check ground connections: Verify the burner assembly and control board ground wires are tight and free of rust. Clean contact points with emery cloth if corroded.
• Inspect burners: Remove burners if accessible. Clean rust and debris from burner ports with a wire brush. Ensure the crossover ports between burners are clear.
• Verify gas supply: Confirm other gas appliances operate normally. Low gas pressure requires utility or technician service.

If the furnace still loses flame signal mid-cycle, a technician should measure microamp flame current and adjust or replace components as needed.