High Lockout
Fast flash / Flashing on Worcester Bosch 28i RSF

Your boiler's internal computer has developed a serious fault and can no longer control the heating or hot water safely.

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

Internal fault - Replace control board

What causes this fault?

This fault occurs when the boiler's central brain, the printed circuit board, fails its internal safety checks or loses communication with the sensors. The most common reason is electrical degradation of the components over time, or a loose connection in the wiring harness that prevents the system from operating 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.

Find a Gas Safe engineer
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