Boiler shuts down and displays E02, burner stops shortly after ignition attempt

Safety warning: Turn off power and gas before opening the combustion chamber. Allow the boiler to cool completely.

Steps to troubleshoot:

• 1. Observe the sequence: Restore power and call for heat. Watch through the sight glass: does the burner light and then go out within a few seconds? If yes, flame sensing is suspect.
• 2. Clean flame sensor: Shut power off again. Remove the flame sensor rod from the burner assembly. Lightly polish the metal rod with fine steel wool to remove oxidation. Do not sand the ceramic insulator. Reinstall and ensure it is fully in the flame path.
• 3. Inspect burner and orifices: Remove the burner rack if accessible. Check for rust flakes, soot, or debris blocking the burner ports. Clean with a soft brush and vacuum. Do not enlarge orifices.
• 4. Check gas supply stability: Confirm that other gas appliances are not causing pressure drops (e.g., multiple large appliances starting simultaneously). A technician should verify inlet pressure with a manometer.
• 5. Wiring and ground: Ensure the boiler chassis is properly grounded and all flame sensor and ignition control wires are tight and undamaged. Poor grounding can cause false flame loss detection.

Call a technician if: E02 continues after cleaning and visual checks, or if flame appears normal but the control still drops out. The gas valve or control board may require professional testing and replacement.