Must admit, I’m a bit baffled as to why increasing the DT results in fewer defrosts and less cycling (by the looks of things). I would assume that an increased DT also results in lower SCOP as the flow temp has to be increased to acheive the same leaving water temperature. @agileoctopus which system is yours on HPM I’d be interested to have a look? I’ve got a 6kW altherma currently.