U4-66 High
Your boiler's internal components have stopped communicating with each other, meaning the system cannot send or receive the signals needed to run.
Technical description: CAN-bus timeout
Typical repair cost: £150-£450 (including labour)
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Protect yourself from future repair bills
A boiler cover plan would cover faults like U4-66 — no call-out fees, no surprises.
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Parts commonly replaced
- Wiring harness
- Main PCB (Printed Circuit Board)
- User interface display board
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