I have a power shower that used a Watermill 2bar pump. The supply for cold comes from tank in the roof space. The supply for the hot comes off the 22mm running down beside the hot cylinder. The last guy did not put a flange on as the cylinder has only got a 22mm male thread brazed on top and as the cylinder was not new he didnt take a chance drilling the side. The supply for the shower runs back into the roof space at roughly the same height as the water in the cold tank. Somehow he managed to get a flow otherwise the pump would not have kicked in, or could he have primed the system in some way? Anyway there is no flow now, the pump just fitted wont kick in. (Techflow) Now this system worked for three years before I got the call because the pump was not working. Would you suggest a negative head pump? And can anyone tell me how he got the shower to work in the first place. Cheers! PS the shower valve is a Bristan Prism.