Wd72 wont fill with water and states error E15 but no blockage anywhere !?

Hi
We are having a problem with our WD72, we keep getting an error message (E15) and states we should check outlet pipes, we have checked thoroughly and have cleared all small items left in pipes but now machine wont fill with water, when a programme is selected the drum starts to move gently round as normal but no water goes in and after a few minutes it beeps and says check outlet pipes...........Very annoying!!!
Any help would be gratefully recieved