Try the following:
1. Take out and clean the filter, separating it into two parts first - if there are two parts in your model.
2. Take off the two rotors; run tap water through each of them in turn, injecting the water through the central inlet; the water should stream freely out of all the little exit slots. If any are blocked by tiny food or gunge particles, remove these, say with a piece of fine wire, needle, or other implement.
Tro, August 2010