The goal of this paper is to minimalize the gap between the heat pump’s compressor COP and the system COPs. A water-water heat pump was installed in a family house without piped floor heating, with 13 radiators, together with a 300 litres thermal storage and 200 litres hot water storage tank. Some measurements are published, taken before and after the system optimisation. The measured compressor COP is compared with theoretical data published by the device producer. The results show that the power consumption was decreased by 15 percent after the system optimisation. The influence of the equithermal curve settings and the power of the submersible pump are analysed and the results are presented. The seasonal COP (SCOP) for Bratislava area is calculated. for the system under consideration.