High
B illuminated continuously on Alpha CD18 / CD24

Your boiler has tried to start but could not ignite the flame, so it has locked itself out for safety.

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

Burner has failed to light. Rotate selector switch to reset position (3) and the ignition sequence will restart after a delay of about 30 seconds.

From this model's manual
Verified against the Alpha Cd 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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