I have a bath mixer with shower facility which works off a combi boiler - water gets too hot when someone turns on a cold tap elsewhere in house. I would like to fit a thermostatic mixer valve onto the pipework supplying the shower, can someone explain how these are plumbed in ? They seem to have two inlets for hot and cold but only one outlet for mixed . Does this get plumbed into hot tap ? if so does the cold have a direct supply separate from that supplying the valve? I have looked at a manufacturers fitting instructions but they don't appear to be as basic as I need. Any simple explanation gratefully received.