Your boiler has entered a safety lockout mode because it failed to light or stay on properly after multiple attempts.

Non - Volatile Lockout

What causes this fault?

This fault occurs when the boiler's control system detects that a flame has not been successfully established or maintained after several ignition cycles. The most common reasons include a worn-out spark probe that can no longer ignite the gas, or a faulty gas valve preventing fuel from reaching the burner.