Furnace starts, burners light briefly, then shut off with E03 code

Safety first: Disconnect power and shut off gas before touching gas components.

• Clean flame sensor: Remove and clean the flame sensor rod with fine abrasive pad as described for E02. Ensure the mounting surface is clean to provide a good ground.
• Check ground connections: Locate the green ground wire from the control board to the furnace chassis and burner rack. Tighten any loose screws and clean off rust or paint under the ground lugs.
• Inspect burners: Remove burner assembly if accessible. Clean rust, scale, or debris from burner ports with a soft brush and compressed air. Ensure burners are properly seated and aligned with the ignitor and flame sensor.
• Monitor gas supply: If other gas appliances flicker or go out, there may be a supply or regulator issue. Contact your gas provider.
• When to replace: If flame repeatedly drops out mid-cycle despite clean sensor and good ground, the gas valve or control board may be failing. Replacement of the gas valve should be done by a licensed technician due to leak and combustion risks.