BoilerFaultCodesYour boiler's internal components have stopped communicating with each other, meaning the system cannot send or receive the signals needed to run.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: CAN-bus timeout
What causes this fault?
This fault occurs when the electrical connection between the boiler's internal computer and its control panel is broken or interrupted. The most common reason is a loose or damaged wiring bridge, but it can also be caused by moisture ingress or a component failure on the circuit board itself. Because these parts can no longer 'talk' to each other, the boiler shuts down as a safety precaution.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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A boiler cover plan would cover faults like U4-66 — 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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