High Lockout
F63 on Glow-worm Flexicom sx

Your boiler's main internal computer has developed a communication failure, meaning it can no longer control the heating and hot water functions.

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

Main PCB fault

What causes this fault?

This fault occurs when the boiler's main control board suffers an internal component failure or a memory error, preventing it from processing instructions. It is often caused by general electrical wear and tear over time or a sudden power surge that damages the delicate circuitry on the board. In some cases, loose or damaged wiring between the board and other internal components can also trigger this communication breakdown.

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

F61View →F62View →F64View →F65View →F67View →

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