I am a bit confused about the workings of a combi boiler, which i hope someone can enlighten me. When a combi boiler loses pressure on the central heating loop, which is closed, it has to be be repressurised. I can fully understanfd that, howegver when the pressure drops to about 0.5 the hot water part of the combi fails to heat the water for the kitchen, etc. Why is that, i would have thought the hot water operation was independant of the ch pressure, working like an old fashioned ascot heater. Can someone explain this , thanks