BoilerFaultCodesYour boiler's fan is running continuously or failing to stop, which prevents the system from starting a new heating cycle safely.
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 should be stationary. The most common reason is a communication error between the fan and the main circuit board, often caused by a faulty internal switch or a sticking relay that keeps the power flowing to the motor.
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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Worcester Bosch Greenstar 25i (ZWB 7-25) 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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