Furnace indicates ignition lockout after multiple failed ignition attempts.

Safety first: Turn off power and gas before servicing burners or ignition components.

Steps:

• Reset the furnace by turning power off for 30 seconds, then back on. Observe the ignition sequence through the sight glass.
• If you see gas but no ignition, inspect the CTC hot surface igniter for correct position relative to the burner ports. Adjust mounting if necessary per service manual.
• Clean burners and crossover ports to ensure flame can travel smoothly from burner to burner.
• Check that the gas supply shutoff is fully open and that other gas appliances in the home operate normally (indicating adequate supply).
• If lockouts persist, the ignition control section of the CTC integrated control board may be faulty and require replacement by a professional.