Your boiler is failing to detect a flame after it tries to start, meaning your heating and hot water will not work.

FAULT: THE BURNER LIGHTS BUT THEN GOES OUT. THERE IS NO FLAME DETECTED. / THE BURNER DOES NOT LIGHT AT ALL, BUT THERE IS AN IGNITION SPARK.

What causes this fault?

This fault occurs when the boiler tries to ignite but fails to confirm that a steady flame has been established, causing the system to shut down for safety. The most common reasons are a buildup of carbon on the sensing probes or a fault with the gas valve preventing fuel from reaching the burner. It can also be caused by an unstable gas supply or a worn-out ignition lead failing to carry the spark.