G4920SC Miele Dishwasher F24 error code

Good Morning everybody, I have a customer with a G4920SC Miele Dishwasher which is going through the wash cycle and is fine until the last 5 minutes (drying cycle) and then comes up with a F24 error code and the inlet/drain and the rinse aid light flash. It is heating the water fine which is normally what the F24 error code means. Has anybody got any ideas ?? Thanks for looking at this query Regards Neil