High Lockout
C1 on Worcester Bosch Greenstar 12i System

Your boiler's internal fan isn't spinning fast enough to safely clear away exhaust fumes, causing the system to shut down for your protection.

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

Airflow stopped during operation

What causes this fault?

This fault occurs when the boiler's control system detects that the internal fan is spinning slower than the required safety threshold. The most common reason is a buildup of dirt or mechanical wear within the fan motor itself, though it can also be caused by loose electrical connections or a failing control board failing to send the correct signal.

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

C4View →C6View →A1View →

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