High Lockout
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.

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 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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Related fault codes

C1View →C6View →A1View →

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