All of the dishwashers sold today have safety switches that prevent them from running if the door doesn't lock properly, but you can probably fix this problem on your own with a little guidance. If your dishwasher won’t lock, there’s likely a problem with the door lock mechanism, also simply called a latch, or the catch. Before you start working, be sure to disconnect the power to your dishwasher so you don’t risk electrical shock.
You'll need to access the faceplate and locate the door lock mechanism. Remove the screws from the top of the door in order to access the faceplate which houses the door lock mechanism. Slide the faceplate out and free the wiring from its clips to give you more room to work. Locate the door lock mechanism at the top, center of the faceplate.
Sometimes, the issue is that the screws that hold the locking mechanism have loosened over time, allowing it to shift slightly. This prohibits the door from locking. To adjust the door lock mechanism, loosen the screws that hold the latch in place, but don’t remove them completely. Adjust the placement of the latch, and close the door to see if it locks properly. If it does, you can tighten the screws and test your work by starting the dishwasher.
If the dishwasher doesn’t start after adjusting the locking mechanism, you can safely assume that it is faulty. In this case, purchase a new locking mechanism at your local home store or from the manufacturer of your dishwasher. Remove the screws and the old door lock mechanism. Put the new latch in place and tighten the screws, then re-attach the faceplate.
If adjusting or replacing the door lock mechanism doesn’t fix your problem, the issue may be a faulty catch. The catch is the piece of metal that clips into the locking mechanism to hold the door shut; they can be purchased at home stores or via the manufacturer. To replace the catch, remove the screws that hold the top of the dishwasher in place, and locate the catch. Remove the screw that holds the catch in place. Replace it with a new catch in the same manner as you removed the old one, and then replace the top of the dishwasher.