F.12 High
Your boiler has detected a internal blockage that is preventing water from flowing correctly and affecting the pressure.
Technical description: A blockage in the appliance is affecting the system’s pressure.
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 F.12 — no call-out fees, no surprises.
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Parts commonly replaced
- Main Heat Exchanger
- Secondary Heat Exchanger
- Pump
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