BoilerFaultCodesYour boiler's computer brain has encountered a serious internal error and can no longer control the heating or hot water safely.
Book a Gas Safe engineer within 24–48 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 fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
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A boiler cover plan would cover faults like E42 — no call-out fees, no surprises.
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Parts for discontinued models can be hard to find and expensive. A new A-rated boiler could save you money on both repairs and energy bills.
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