High
lock-out on Worcester Bosch Greenstar 15i System

Your boiler is failing to light the flame, so it has safely shut itself down to prevent a gas leak.

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.

What the manual says

Manufacturer manual

The burner will go out but, after a short pause, the appliance will attempt to restart and spark for 10 seconds and then 'lock-out'. Occurs if the gas service cock is turned off or if the burner does not light and is not sensed by the control circuit.

From this model's manual
Verified against the Worcester Bosch/Worcester Bosch Greenstar I System installation & service manual.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

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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All 16 fault codes on the Greenstar 15i System

Seeing a different code? Every code this model can display, in one place.

Blue light: Off / Lockout: OffBlue light: On / Lockout: OffFan does not runFlue overheatIgnition lockoutInternal faultLOCKOUTNot a fault codeSI1SI2SI3ST6ST10ST19Volatile lockout

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