Your boiler is having trouble communicating with the internal pump that manages one of your heating circuits, meaning that part of your heating may not be working correctly.

Communication fault - variable speed heating circuit pump, heating circuit M2. Control mode, max. pump speed

What causes this fault?

This fault occurs when the boiler's main control board loses its digital connection with the pump responsible for your secondary heating zone. The most common reason is a physical failure of the pump's internal electronics or a loose connection in the wiring that carries signals between the components.