Apologies if this has been covered before but I have a problem with our 15 year old Bosch dishwasher in that it only seems to clean the soiled items in either the top or bottom racks but is not consistent. I have done the obvious and cleaned the filters and spray arms etc and actually replaced the microfilter as it had started to split, I’ve also removed the covers and see nothing that appears wrong to a more or less layman. I presume as the pump is spinning freely that it should be circulating water through both spray arms simultaneously? Any help appreciated, I know its old but fundamentally the machine is still very good. Many thanks in advance.