Your boiler has tried and failed to start up five times in a short window and has now locked itself out for safety.

Ignition lockout - 5 restart attempts within 15 minutes

What causes this fault?

This fault occurs when your boiler detects that it has lost its flame five times within a fifteen-minute window, forcing it to stop running to ensure your safety. The root cause is usually a failure in the ignition process, meaning the boiler can't reliably light the gas or recognize that a flame is present. This is often caused by a worn-out ignition spark, a faulty sensor, or an inconsistent flow of gas to the burner.