Hi my name is ***** ***** as you are aware the inlet valve and pump are interconnected at the back. First thing to do is take off the back panel and gently pull the valve/pump assembly backwards. once you have done this with help get someone to press the water supply and see if you have got any suck on the pump inlet side. If not you have a faulty pump, if the pump appears to be sucking then its either the valve or an air leak in the pipes.
No worries - let me know how you get on, in the meantime would you kindly rate the information given sofar, once done all further questions are free of charge, come back to me on Friday if you need further help - Ian