Hello, I've got a persisting problem with my shower. The pump would not start unless I "bleed" a bit of water out from one of the outlets of the pump. I have fitted check value to the hot water outlet, auto air vents to the highest points between the pump and the thermostatic value and raised the c/w tank to male sure there is no negative head situation. Also I've bypassed the pump at one point and there is water running almost enough to have a shower (perhaps about 3-4l/min). I am totally stuck with no ideas what could be the problem. Would appreciate any suggestions.