Your boiler is having trouble communicating with the internal pump that moves water around your radiators, which may lead to your heating not working effectively.

Communication fault - variable speed heating circuit pump, heating circuit A1. Control mode, max. pump speed

What causes this fault?

This fault occurs when the boiler's main computer loses its digital connection with the high-efficiency circulation pump. The most common reason is a technical glitch in the pump's internal electronics or a loose connection in the wiring that carries speed signals. Without this communication, the boiler cannot safely coordinate how fast water should move through your radiators.