BoilerFaultCodesYour boiler's fan is running constantly or at the wrong time, which is usually caused by a safety component failing to tell the fan when to stop.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Fan does not switch off.
What causes this fault?
This fault occurs when the boiler's control system detects that the fan is spinning even when it shouldn't be, or the air pressure switch is stuck in the 'on' position. The most common reason is a mechanical failure within the air pressure switch or a communication error from the main circuit board that prevents the fan from shutting down safely.
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 C4 — no call-out fees, no surprises.
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