Boiler shows E11, ignition may start but lockout occurs, sometimes associated with ionisation fault

Safety first: Turn off power and gas. Combustion checks must be done by a qualified engineer.

• Reset once: If E11 appears sporadically, reset and observe. Persistent E11 requires investigation.
• Clean flame electrode (engineer task): Remove the electrode and gently clean with fine abrasive paper to remove oxidation. Check the ceramic for cracks and replace if damaged.
• Check earth continuity: Verify that the boiler casing and burner have a solid earth connection back to the supply. Tighten any loose earth wires.
• Check burner and gas settings (engineer task): Confirm burner is clean and gas pressure/combustion are within Sime limits. Incorrect combustion can cause weak flame signal.
• PCB test (engineer task): If electrode and combustion are correct, the flame detection circuit on the PCB may be faulty and require replacement.