High Lockout
Lockout light on on Ideal Concord Super Series 4

Your boiler has stopped itself for safety because it failed to light or stay running, and it needs to be manually reset.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description

Ignition failure or safety interruption requiring manual reset of the lockout switch.

What causes this fault?

This fault happens when the boiler tries to start but fails to detect a constant, safe flame. It is usually caused by a worn-out ignition spark, a blocked pilot light, or a gas valve that is no longer opening correctly to let fuel into the burner.

Engineer required

This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

Find a Gas Safe engineer
Search the official register →

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