High
C4 on Worcester Bosch Greenstar 30HE

Your 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.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

What the manual says

Manufacturer manual

Fan does not switch off.

From this model's manual
Verified against the Worcester Bosch Greenstar 30he installation & service manual.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

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 is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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