Your boiler has lost its flame while it was supposed to be running, causing the system to shut down for safety.

Illuminates if the burner is extinguished while there is still a demand for the boiler to operate. Indicates a fault if it illuminates repeatedly.

What causes this fault?

This fault occurs when the boiler's control system can no longer detect a flame while the unit is trying to heat your home. It is often caused by a dirty or worn-out sensor that can't see the fire, or a faulty gas valve that isn't providing enough fuel to keep the burner lit. Because the boiler cannot confirm it is burning gas safely, it shuts down entirely to prevent unburnt gas from building up.