Your boiler has failed to ignite, meaning it cannot create the flame needed to provide you with heating or hot water.

Burner failed to light. Check gas supply and gas valve operation. Check fan and spark operation. Check flue for blockage. Clean or replace ionisation probe & lead. Check condensate outlet not blocked & vent tube is clear

What causes this fault?

This fault occurs when the boiler's control system attempts to start the burner but fails to detect a stable flame after several attempts. The most common reasons include a lack of gas reaching the unit, a dirty or worn-out sensor that can't 'see' the flame, or a build-up of debris in the internal components that prevents a successful spark.