A42 High
The boiler's internal thermometer is sending an incorrect signal to the control board, preventing the system from heating your water correctly.
Technical description: Flow sensor error – sensor damaged
Typical repair cost: £120-190 (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 A42 — no call-out fees, no surprises.
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Parts commonly replaced
- Flow temperature NTC sensor
- Sensor wiring harness
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