Kenwood slimline kDW45x13 dishwasher slow going through cycles?

My dishwasher was working fine, then all of a sudden became slower and slower going through a cycle, no warning signs, cleaned filter, checked spinner arm, but don't kno of its the flap and if so how do I get to it???? No parts are visible and no details of problem in instruction manual either, or info on how to fix it! It must be something easy to fix as there are no fault codes coming up! Salt is full, rinse aid is full, made sure pipe is extended high for removing water as I kn that helps, but made no difference, any help would be very much appreciated!