If you haven't already cured it have a look at the inlet pipe for a balance pressure valve turn the top knob clockwise to close it turn a tap on about halfway turn the knob anti clockwise and the pump will come on and when the valve starts to click stop turning the knob and turn the tap off the pump will run on then stop. If you haven't got a pressure valve then I can't say what it is.
Nobby
September 2008