L5 or F5 High
Your boiler has stopped working because it cannot properly measure the temperature of the water returning from your radiators.
Technical description: Return thermistor fault
Typical repair cost: £100-180 (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 L5 or F5 — no call-out fees, no surprises.
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Parts commonly replaced
- Return thermistor (NTC sensor)
- Wiring harness
- Main PCB
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