I'm presuming that the problem i'm having with leaking mixer showers and taps is linked to my change to an unvented indirect system and consequent increase in hot water pressure? Changing cartirdges in the taps seems to have worked and I presume this will be the case with shower mixer unit. But my basic question is: how do you isolate the hot water system? Do you just turn off the stop cock under the sink and that reduces the pressure into the 300 litre cylinder I have and stops forcing the hot water out top (I am a very simple person!)?