last days I wondered if our Vaillant heating boiler is working efficiently. Even when it was very cold outside it did not run continously. The temp rised up to a maximum, not using the minimum power possible, stopping the burner and waiting for cool down of the water. Then starting again - and again...  Sitting in front of the display and writing a protocol on paper for hours was not a solution for me. So I remembered that the system uses a eBus (twisted pair of wires) for communication between