High Lockout
C6 on Worcester Bosch Greenstar 25 HE Combi

Your boiler has detected that its internal fan is spinning at the wrong speed, which means it cannot safely exhaust fumes and has stopped working as a result.

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 speed too high.

What causes this fault?

This fault occurs when the boiler's control system loses the ability to regulate the fan speed effectively, often due to a mechanical failure or an electrical communication error. The most common reason is a failing fan motor or a fault within the main circuit board that prevents it from sending the correct signals to manage airflow.

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 →C4View →

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