Group 1, 5 flashes Emergency

Worcester Bosch Group 1, 5 flashes Fault Code

Also written as GROUP15FLASHES — same fault.

The Worcester Bosch Group 1, 5 flashes fault code means: your boiler has detected a potential internal gas leak or a sensor fault that prevents it from starting safely to protect your home.. 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: Ionisation detected after burner stopped; Gas valve leaking; False flame detected; Gas valve EV2 leak test failed; Gas valve EV1 leak test failed; Ionisation current detected before burner-start; Gas valve error; Ionisation sensor shorted
Typical repair cost £200-450 (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 Group 1, 5 flashes fault code

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

Source

Worcester Bosch Group 1, 5 flashes 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