Boiler lights briefly then shuts down, display shows 'Flame Failure', 'Flame Loss', or similar, often followed by retries.

Safety first: Turn off power and gas before removing burner or combustion covers.

• 1. Clean flame sensor: Remove the flame sensor from the burner assembly. Gently clean the rod with fine emery cloth until shiny. Do not sand excessively. Reinstall and ensure it is fully in the flame path.
• 2. Check grounding: Verify the boiler chassis is properly grounded. Tighten ground screws on the control board and burner assembly. Loose grounds can cause erratic flame sensing.
• 3. Inspect burner: Look for rust, debris, or scale on the burner and in the combustion chamber. Lightly brush and vacuum loose debris without damaging burner ports.
• 4. Verify venting and air intake: Blocked intake or exhaust can cause unstable flame. Clear any obstructions and ensure proper pipe slope and support.
• 5. Monitor operation: After cleaning and reassembly, restore power and call for heat. If flame still drops out, gas pressure or combustion tuning may be off and requires a qualified technician with proper instruments.