Having just completed all new pipe work from the stopcock to the bathroom/kitchen and having installed a new combi-boiler I have noticed a very strange thing with the water flow. When a tap is turned on there is a burst of water then the flow steadies. When the main stopcock, which was fully open, is turned down to a very small little flow the water jumps out and the ordinary flow continues. In the house next door they have the same boiler ect, but this does not happen. This happens on the cold and to a little extent on the hot..