i have the ecoTEC boiler with Vaillant UniSTOR what im wondering is how do i stop the water flowing into pipes in the house as i need to change kitchen tap, do i need to turn stopcock off under sink then drain the full 180 litres out as that seems a bit of a waste or can it be shut off i have looked at the unistor and there is a few stop valves ,well thats what they look like ,but which one is the right one