BoilerFaultCodesYour boiler has detected an issue with how it extracts exhaust fumes, and it has shut down for safety purposes.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: AIR FLOW DEVICE: The appliance will enter a lockout condition in the event of an air flow fault/controls fail to detect the correct air flow.
What causes this fault?
This fault occurs when the boiler's internal safety sensors detect that harmful exhaust gases are not being effectively cleared through the flue pipe. The most common reasons are a failing extraction fan that cannot spin fast enough, a blockage in the air pressure tubes, or a build-up of debris within the venturi system.
This fault often surfaces during the first cold spell of autumn when the fan is forced to work harder after sitting idle over the summer months.
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 Domestic water demand indicator flashes (approximately five times per second) — no call-out fees, no surprises.
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Worcester Bosch 25si and 28si is discontinued — time for a new one?
Parts for discontinued models can be hard to find and expensive. A new A-rated boiler could save you money on both repairs and energy bills.
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