Your boiler has stopped working because it failed to light or stay lit, which has triggered a safety shutdown.

Burner Lockout. Possible causes: gas supply issue, spark electrode/lead failure, gas valve failure, flame sense electrode/cable failure, or control board fault.

What causes this fault?

This fault occurs when the boiler tries to light the burner but fails to detect a stable flame after several attempts. The most common reasons are a lack of gas reaching the unit, worn-out spark components that can no longer create a flame, or a sensor that is too dirty to 'see' the flame once it has started.