Your boiler has stopped working for safety reasons and needs to be reset to try and fire up again.

Indicates a lockout fault; requires pressing the reset switch and waiting 15 seconds between attempts.

What causes this fault?

This fault happens when the boiler attempts to start up but fails to detect a steady flame, causing it to shut down for safety. It is usually caused by a lack of fuel reaching the burner or a component failing to generate the spark needed to ignite the gas. In some cases, the boiler may actually be lighting, but a faulty sensor is failing to tell the internal computer that the flame is present.