Your boiler is having trouble communicating with its internal pump, which means it cannot properly move heated water around your system.

Control mode, max. pump speed: Communication fault - variable speed internal pump

What causes this fault?

This fault occurs when the boiler's main control board loses its digital connection with the internal pump, preventing the system from regulating water flow. The most common reason is a failure in the pump's electronic circuitry or a loose connection in the wiring harness that carries data signals. Without this communication, the boiler cannot safely manage heat distribution and will stop operating to prevent overheating.