High
lock-out on Worcester Bosch 24si II

Your boiler is failing to light the flame, which means it has stopped working to keep you safe.

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 goes 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.

Shared across the 24si II range
This code is shared by the boilers in this range, which use the same control board. It may not be printed in this exact variant’s 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 14 fault codes on the 24si II

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

Air flow faultDHWsensorF1F2Flash 4 times per secondFlash 8 times per secondFlash once per secondIgnition lockoutLED 4 flash/secondLOCKOUTOverheat cut-offWater temperature too coolWater temperature too hot

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