We have a stand alone bath & shower and when first plumbed in worked fine. 2 years on and the hot still comes through every time but the cold (if not left coming out of tap when turned off) fails to come through. When this happens you have to run other taps around the upstairs to bring the water in the bath to come through. Weird as the water for the bath comes from cold water tank in roof with hot coming from cylinder (both supplies in 3/4" copper). After about 10-20mins the cold water starts to come through the bath / shower............Does anyone have any ideas?