Your boiler is currently trying to start up but is failing to detect a flame, meaning it cannot ignite to provide heat or hot water.

Ignition: ignition is activated for 2.4 seconds while the gas valve is opened.

What causes this fault?

This fault occurs when the boiler's internal sensors detect that the water returning from your radiators is hotter than the water leaving the boiler. This usually means the water is physically being pushed the wrong way through the system or a sensor has failed and is sending incorrect data to the control board. It is often triggered by a failing pump or a blockage that has forced the water to circulate in reverse.