BoilerFaultCodesYour boiler has detected a blockage or a fault in the pipe that carries exhaust fumes outside, causing it to shut down for safety.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Flue pressure switch: Blockage in flue system
What causes this fault?
This fault occurs when the boiler's internal safety sensors detect that the exhaust fumes are not being cleared away safely or quickly enough. The most common reasons include a physical blockage in the flue pipe outside, a build-up of debris inside the fan assembly, or a split in the internal rubber tubes that monitor air pressure.
This issue is more frequent during autumn and winter, as fallen leaves or nesting birds can physically block the external flue terminal.
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 Slow flash (normally on, flashes off) - 3 — no call-out fees, no surprises.
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