BoilerFaultCodesYour boiler has detected a problem with how it vents waste gases or takes in fresh air, which is preventing it from firing up safely.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Appliance fault / Air flow fault
What causes this fault?
This fault occurs when the boiler's internal safety sensors detect that the fan isn't moving enough air to safely expel exhaust gases. It is often caused by a buildup of dirt in the small plastic tubes inside the unit, a failing fan motor, or a physical blockage in the flue pipe leading outside. Because the boiler cannot guarantee that harmful fumes are being moved away correctly, it refuses to ignite as a safety precaution.
This issue can become more frequent during periods of high winds, which can create back-pressure in the flue and interfere with the sensitive air pressure readings required for the boiler to start.
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.
Gas Safe Register →Protect yourself from future repair bills
A boiler cover plan would cover faults like FLASHING FAST (five times a second) — no call-out fees, no surprises.
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