Aeg lavamat protex l75480

Every now and then the washer goes through its wash cycle, rinses then it stops showing its completed the cycle but the washer is still full of water and it has not spun the clothes. There are no error messages to be seen. The door lock will open and you can switch from programs and lock the door again but it will not start, so if you try to set it for the rinse and spin cycle press the start, the door locks but it just sits there doing nothing. after about ten tries it does eventually start. I have checked the pump and cleaned the filter, the drain is OK, it might be OK for three or so washers then on the four it fails to empty and spin although the cycle is indicating its complete, anyone any ideas?