Your boiler is currently performing a normal startup sequence and is operating at its initial ignition power level.

The burner operates at ignition load in heating or domestic hot water mode

What causes this fault?

This code appears because the boiler has been manually or automatically triggered to run at its lowest possible firing rate. It is an intentional test mode used to check the stability of the flame and the accuracy of the gas valve settings. Since it is a controlled test rather than a mechanical failure, your boiler will return to normal operation once the program finishes.