dishwasher hasnt enough water?

the aeg 4020 isnt getting enough water, it shoots halfway up the back pipe and almost cavitates. If I prime it before by filling the inside with 2 jugs of water it works, and the water shoots up
but I have to do this before the wash cycle and before the rinse cycle. I have tipped the machine upside down stripped the pump and all the pipes nothing is blocked. The water inlet valve is difficult to blow air through, and I am assuming water cant get through either, unless there is a sensor here and when the machine is on that part of the cylce it opens the valve....it doesnt seem to open long enough.could this be the problem?