Safety: Isolate power and gas before removing the boiler case. Gas work must be carried out by a Gas Safe engineer.

User checks:

Attempt a single reset from the control panel. Do not repeatedly reset a boiler that fails to ignite.
Ensure flue terminal is not blocked by debris, snow, or vegetation.

Engineer checks:

Inspect and clean the flame sensing electrode on the Keston burner using a non-abrasive pad. Ensure correct gap and positioning as per Keston technical data.
Check the burner and combustion chamber for heavy soot or debris that could affect flame stability; clean or replace burner head if required.
Verify all earth connections between burner, chassis, and PCB are secure and free of corrosion.
Measure flame rectification current according to Keston service manual; if low, suspect PCB flame circuit or electrode/lead issues.
Check combustion with a flue gas analyser and adjust or replace the gas valve if gas/air ratio is out of specification.

Boiler locks out with E02, fan runs briefly then stops, no flame

Possible Causes