High Lockout
17 on Glow-worm EnergySaver Combi

Your boiler's main control computer has developed an internal electrical fault and can no longer safely operate the system.

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 internal computer suffers a hardware failure, meaning it can no longer process data or send signals to other components safely. The most common reason is typical wear and tear on the electrical circuitry or a sudden power surge that has damaged the delicate components on the control board.

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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