F.12 and F.91 High
Your boiler has lost its ability to monitor the temperature of your hot water cylinder because a sensor has developed an electrical fault.
Technical description: Cylinder temperature sensor short circuit
Typical repair cost: £90-160 (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 F.12 and F.91 — no call-out fees, no surprises.
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Parts commonly replaced
- NTC Cylinder Temperature Sensor
- Sensor Wiring Harness
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