How to repair or fix a Dishwasher if it doesn't wash well
A common cause of poor washing results is improper loading—dishes that block or impede the spray arm(s) or prevent the soap dispenser from opening. On the other hand, if your dishwasher has chronic problems with good washing, the problem may not be your dishwasher. A good first step is vary the amount of dishwasher detergent you're using and try switching brands.
Other possibilities: Your home’s water pressure may be too low, your water may be too hard, or the water temperature may not be hot enough.
In order for your dishwasher to fill to the appropriate level, water pressure should be from 20–120 pounds per square inch. If you suspect that your water pressure may be low, turn off all faucets or other users of water (such as washing machines and sprinklers) and then put a half-gallon jug under the kitchen faucet. Turn on the hot water full-blast. If the jug doesn’t fill within 14 seconds, your water pressure may be too low for proper dishwasher operation. Call your city water utility to discuss your options, or avoid drawing water elsewhere in the house or yard during dishwasher cycles.
The right amount of detergent to use depends on how large your load of dishes is and how hard your water is. Hardness is measured in grains of minerals—the more grains per gallon you have, the more detergent you’ll need. If your water has 12 grains or more of hardness, fill both dishwasher soap cups completely with detergent. If that doesn’t work, consider installing a water softener.
To check water temperature, hold a meat thermometer under the hot water faucet for two minutes; if it doesn’t register a minimum of 140 degrees F., turn up the temperature dial on your hot water heater. (However, if you have a newer dishwasher that heats the water internally, it isn’t necessary to turn up your hot water heater.)
If your dishwasher has worked fine in the past but suddenly your dishes aren’t clean after the dishwasher completes all cycles, listen to the spray arm(s) spinning inside during the wash cycle. If spinning poorly, wait for the machine to cool down, remove the spray arm(s) by unscrewing the hubcap(s), lifting the arm(s) off, and then cleaning out the spray holes in the spray arm(s) with a stiff piece of wire.