Boiler displays E1 227, attempts to ignite but fails, then locks out.

Safety first: Isolate electrical power and do not attempt to adjust gas components yourself.

• Reset once: Press reset and observe whether the boiler lights briefly. If it repeatedly fails, do not keep resetting.
• Check supply polarity: Ensure the boiler is wired correctly at the fused spur (L, N, E). Incorrect polarity can prevent flame detection and must be corrected by a qualified electrician.
• Check gas supply: Confirm other gas appliances work. If not, contact your gas supplier.
• Visual inspection: Ensure the flue terminal is clear and condensate pipe is not frozen or blocked.
• Engineer tasks: A Gas Safe engineer should clean or replace the flame sensing electrode, verify earth continuity, check burner and combustion, and test gas valve operation and inlet pressure.