What does 7 prewash flashes indicate?

My Bosch WFF20.. Gets to a point in the wash cycle and then clicks on through , then stops with the prewash flashing 7 times. I know it isn't rinsing because the conditioner is still in the drawer, but I can't catch at what point it goes wrong. Annoyingly sometimes it's fine but others it's not and there seems to be no pattern. As a lady on her own I would like to have some idea of whats wrong and what it should cost to fix if possible. Sorry guys but I'm fed up being ripped off