Bosch Exxcel - lack of cleaning power in bottom tray?

The dishwasher has been given a good clean and there does not appear to be any reason why, saucepans in particular, do not get cleaned when on the bottom tray. It is as if no water reaches under the saucepans, as if no water is sprayed up from the lower arm although there is no blockage in it. Any suggestions would be much appreciated. Many thanks