BoilerFaultCodesYour boiler has detected a internal blockage that is preventing water from flowing correctly and affecting the pressure.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: A blockage in the appliance is affecting the system’s pressure.
What causes this fault?
This fault occurs when the internal pressure sensor detects a sudden drop or spike caused by a lack of water movement. It is usually triggered by a physical blockage in one of the heat exchangers or a failing pump that can no longer push water through the narrow internal pipework. This effectively chokes the system, causing the boiler to shut down to prevent overheating.
This issue often surfaces in autumn when the heating is turned back on after summer, as settled debris in the system is suddenly shifted into the boiler’s narrow components.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
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A boiler cover plan would cover faults like F.12 — no call-out fees, no surprises.
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