BoilerFaultCodesYour boiler has detected an issue with the air flow or the internal fan that clears away waste gases.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Domestic pressure test point
What causes this fault?
This fault occurs when the boiler's safety sensors detect that waste gases are not being effectively cleared from the combustion chamber. The most common reason is a failing internal fan or a blockage in the flue pipe, which prevents the system from ensuring it is safe to ignite.
This fault is more common during periods of high winds, as strong gusts can sometimes obstruct the airflow through the flue and trigger a safety shutdown.
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 A4 — no call-out fees, no surprises.
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Worcester Bosch WR325 RSF 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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