Your boiler has detected a sequence of ignition or flame detection errors and has shut itself down for safety.

Burner control switches to lockout

What causes this fault?

This fault occurs when the boiler's internal computer fails to detect a reliable flame during the ignition process. The most common reasons are worn-out sparks that can no longer light the gas, or a dirty sensor that cannot 'see' the flame even after it has started. It can also be caused by a lack of gas reaching the burner due to a faulty valve or a blockage in the air supply.