Slow flash (unspecified rate) Emergency

Worcester Bosch Slow flash (unspecified rate) Fault Code

Also written as SLOWFLASHUNSPECIFIEDRATE — same fault.

The Worcester Bosch Slow flash (unspecified rate) fault code means: your boiler has detected that it cannot safely get rid of exhaust gases, so it has stopped working to prevent a buildup of dangerous fumes.. It appears on 1 Worcester Bosch model in our database.

Act immediately

Turn off your boiler and stop using gas appliances. Call a Gas Safe engineer now. This fault can be dangerous if ignored.

Technical description: Flue pressure switch: Blockage in the flue system.
Typical repair cost £120-250 (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 Slow flash (unspecified rate) fault code

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

Source

Worcester Bosch Slow flash (unspecified rate) 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