What are the most important things to check if the dishes aren't getting clean?

The first thing you need to check when troubleshooting a dishwasher is to make sure the machine is getting enough water and that it is heated properly. Without enough water the wash arms won't rotate, the cycle will take longer, there could be spots or grit left on the dishes, and, on some older models, the soap dispenser won't open. The fill cycle for most dishwashers is timed, so if there is sediment build-up in the water inlet valve, you will not get enough water in the machine. You can easily check for a low fill problem by adding a large bowl of water during the fill cycle. If the dishwasher works properly after adding the water, you have confirmed the source of the problem. Also, make sure your unit isn't draining while washing (something may be caught in the drain or drain valve), then check to be sure there is adequate water flow to the water inlet valve underneath the dishwasher. If the valve is not letting enough water into the dishwasher, the water inlet valve will most ...  more