Fast flash / Flashing High

Worcester Bosch Fast flash / Flashing Fault Code

Also written as FASTFLASHFLASHING — same fault.

The Worcester Bosch Fast flash / Flashing fault code means: your boiler's internal computer has developed a serious fault and can no longer control the heating or hot water safely.. It appears on 4 Worcester Bosch models in our database.

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 the Worcester Bosch Fast flash / Flashing 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.

Typical repair cost £280-450 (including labour)

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Worcester Bosch models that show the Fast flash / Flashing fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Worcester Bosch Fast flash / Flashing fault code information on this page is sourced and cross-checked against the official Worcester Bosch service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026