High Lockout
F13 on Glow-worm Ci Plus

Your boiler's main internal computer has developed a memory or communication error and can no longer control the heating system 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

Main PCB fault

What causes this fault?

This fault occurring means the boiler’s internal computer has suffered a serious electronic failure and can no longer process data correctly. It is often caused by a physical component failure on the circuit board or loose wiring connections that disrupt the flow of information. Factors like age, heat stress over many years, or power surges are the most likely reasons the board has stopped working.

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

F1View →F12View →F15View →

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