High Lockout
C4273 on Worcester Bosch CDi Classic

Your boiler has stopped working because the internal fan has been running non-stop for too long, causing the system to shut down for safety.

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

Continuous fan operation for the last 24 hours – appliance temporarily blocked

What causes this fault?

This fault occurs when the boiler's control system detects that the internal fan has been spinning continuously for a full 24-hour period without a break. This is usually caused by a communication error between the main circuit board and the fan, or a faulty component that is sending a constant 'on' signal even when heat isn't required. To prevent damage to the motor or overheating, the boiler safety software triggers a temporary shutdown.

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

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