High Lockout
26 on Glow-worm EnergySaver Combi

Your boiler's electronic brain has developed a software or hardware error and can no longer control the heating and hot water safely.

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

There is an internal fault in the Automatic Control Module.

What causes this fault?

This fault occurs when the boiler's main control board suffers an internal hardware failure or a memory error in its programming. It most commonly happens due to electrical wear over time, but can also be triggered by a sudden power surge or dampness affecting the circuitry.

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.

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