Your boiler has failed to light, which most likely means the gas supply is interrupted or there is a blockage preventing the burner from starting.

Flame not detected.

What causes this fault?

This fault occurs when the boiler attempts to ignite several times but fails to detect a flame, causing the system to shut down for safety. The most common reasons include a lack of gas reaching the burner, worn-out spark electrodes, or a buildup of carbon on the sensor that 'sees' the flame.