There are few things more frustrating than reaching into your dishwasher after a cleaning cycle only to find that half of the dishes remain dirty. When dishes on the top rack of a dishwasher are not getting clean, the reason is either human error or machine malfunction. If changing your dishwasher loading habits doesn't result in clean top-rack dishes, you may need to consult a repair service.
As tempting as it may be, do not overstack or overfill your dishwasher. The wash water and soap need plenty of room to circulate, and stuffing the dishwasher beyond capacity impedes this process. Most dishwasher water jets are situated on the bottom, meaning gaps between dishes, pans and cutlery are essential for water to reach the top rack. Examine your dishwasher to learn how the water jets function. If your model has a jet that juts up from the bottom during a wash cycle, keep all bottom-rack dishes clear of this area. Also, refrain from stacking dishes on top of each other. Use the rack pegs as a guide for how to stack your dishwasher efficiently, and make sure the opening or soiled side of the items face toward the centre, where the water sprays the hardest. Check your dishwasher model's instruction manual; many manuals include recommended stacking procedures.
If your dishwasher isn't overfilled, your behaviour could still cause the top rack to remain dirty if you're not rinsing the dishes. While newer dishwasher models do not require a pre-wash, it is still beneficial to rinse off bigger food pieces, liquid pools and crumbs. A light rinsing allows your dishwasher to reach the surfaces of the dishes more easily and prevents filter clogs. The bottom-rack dishes may get clean without a pre-rinse because they are closer to the water jets.
Dishwashers clean dishes by blasting hot, soapy water at them. If the water is not hot enough, dishes will not get clean. The top rack suffers because the more powerful water usually hits the bottom-rack dishes. Check your hot water heater and set the temperature at 54.4 to 60.0 degrees C minimum. If your dishwasher model allows you to select a temperature setting, pick the hottest option and observe whether this change gets your top-rack dishes clean. Before each dishwasher cycle, run your sink's hot water until a high-temperature stream emerges. This helps bring very hot water into your dishwasher right away.
Holes in the water jet arms are likely to clog eventually, especially if you regularly wash dishes without pre-rinsing items. Inspect the water jets for signs of blockages over the holes, and gently scrape out any debris with a toothpick or safety pin. You can also run a cycle of dishwasher cleaner, a specially formulated cleanser that works to unclog water jet holes and remove hard mineral build-up. Dishwasher cleaner is available in hardware and grocery stores.
Water Inlet Valve
A dishwasher's water inlet valve supplies water to the dishwasher. A faulty valve could block some or most water from the unit, reducing the cleaning power. The top-rack dishes suffer the most since gravity works against them getting clean from a diminished water supply. The water inlet valve is usually located behind the lower access panel at the bottom right or left of the dishwasher. The valve looks like a rubber tube jutting from the main water line with two wires attached. Carefully inspect the valve for signs of damage. Also, listen during the dishwasher cycle for what is known as a "water hammer" sound -- pressure surges and stops that cause the water to make a hammering sound during the cleaning cycle. As the valve involves electricity, repairs and replacements are best left to professionals or people with experience repairing appliances.