Whirlpool dishwasher not cleaning contents?

My whirlpool ADG644ix runs through its cycle, the dispenser door opens and there is no obvious sign of a fault. water is entering the washer and the heater is working. I'm not sure how much water is entering or how hot it is getting. At the end of the cycle, the cutlery and crockery is wet and hot but by no means properly clean. The pump does sound a bit more noisy than before but off the machine it seems to run OK.