Originally Vaillant EcoTEC Pro appliances were fitted with a 3 wire pump, however this pump has been superseded by the manufacturer to a 5 wire pump.
EcoTEC Pro appliances operate correctly with the 5 wire version fitted as the PCB is not programmed to use the other 2 wires.
However for resistance checking purposes the readings differ.
Does the appliance have a 3 or 5 wire pump assembly fitted?