Your boiler has developed an internal electrical fault that is preventing it from restarting even after you try to reset it.

Selector switch or PCB failure (Section K)

What causes this fault?

This fault occurs when the boiler's internal computer or the main control dial fails to communicate correctly, meaning the system cannot clear its memory of a previous error. The most common reason is that the circuits on the main control board have worn out or shorted, preventing the reset signal from reaching the burner.