Boiler locks out with E02, no heating or hot water, fan may start briefly then stop

Safety: Isolate power and gas before removing any covers. Flame sensing and combustion checks must be carried out by a Gas Safe engineer.

• Attempt a reset: Use the front panel reset control. If E02 returns repeatedly, do not continue resetting.
• Check for obvious flue issues: Ensure the Main boiler concentric flue is intact, properly supported, and not obstructed at the terminal.
• Check system pressure: Confirm the pressure gauge is within the green band (typically 1.0–1.5 bar when cold). Low pressure can affect ignition stability; top up via the filling loop if needed.
• Engineer actions:
  • Remove and clean the ionisation probe on the Main burner assembly with fine emery or scotch pad; avoid damaging the electrode.
  • Check the burner and combustion chamber for heavy soot or debris and clean as required.
  • Verify good earth continuity between burner, chassis, and earth terminal.
  • Use a flue gas analyser to confirm correct combustion and adjust gas valve (if adjustable) to Main’s specifications.
  • Test the flame detection circuit on the Main control PCB and replace PCB if out of spec.