Your boiler is not in a fault state; it is simply running a pre-programmed test to check how it performs at its lowest power setting.

Minimum load test program

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.