BoilerFaultCodesYour boiler has experienced an internal communication error or processor glitch that is preventing it from running properly.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Internal fault
What causes this fault?
This fault occurs when the boiler's internal computer experiences a breakdown in communication with its own components or sensors. It is usually caused by a hardware failure within the main control board or a loose connection in the internal wiring, meaning the boiler can no longer verify it is safe to operate.
DIY fix possible
Locate the power switch or fused spur for the boilerTurn the power off, wait for 30 seconds, and turn it back onPress the 'Reset' button on the boiler control panel once
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Protect yourself from future repair bills
A boiler cover plan would cover faults like b5 — no call-out fees, no surprises.
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Could it be time for a new boiler?
If repair costs are adding up, a new energy-efficient boiler could be the smarter long-term choice.
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