Your boiler is failing to detect a flame after it tries to ignite, meaning it will not stay lit to provide heating or hot water.

No or insufficient ionisation flow.

What causes this fault?

This fault occurs when the boiler's internal sensor fails to detect a steady flame during the start-up sequence, forcing the system to shut down for safety. The most common reasons are a worn-out sensor probe that can no longer 'see' the flame, a faulty ignition cable, or an issue with the gas valve not delivering the correct amount of fuel.