High Lockout
03 on Glow-worm EnergySaver Combi

Your boiler's internal computer has encountered an electronic 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 main control board's internal circuitry fails, meaning it can no longer process data or send signals to parts like the pump or fan. The most common reason is electronic component fatigue over time, or sometimes a power surge that damages the sensitive microchips on the 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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Related fault codes

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