High Lockout
E42 on Potterton Powermax HE

Your boiler's computer brain has encountered a serious internal error and can no longer control the heating or 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

Internal control error. Switch OFF/ON at mains isolator. Replace boiler control Part No. 5107535

What causes this fault?

This fault occurs when the boiler's main electronic circuit board suffers a critical internal failure, meaning it can no longer process data or manage safety checks correctly. It is usually caused by the natural degradation of electrical components over time or a sudden power surge that damages the board's memory.

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

E40View →

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