I have a problem with my 10 year old Vokera combi. Although the hot water thermostat is on max, the hot water temperature only gets warm, yet the radiators also come on even though the central heating is set to off (summer mode). Possible problem with the DHW flow device as the pin is sluggish activating the flow switch, or maybe the DHW heat exchanger, or both. Any ideas, before I call the experts!