While installing dishwasher dropped screw under spray arm.

There are several reasons that the dishwasher will not drain. There could be a blockage in the filter or the hose. Some dishwasher drain hoses have a check valve in them that can be removed from the end of the hose. If you have recently installed or replaced a garbage disposal then be sure that the cap was removed from the disposal barb where the dishwasher drain connects. Sometimes the entire cap has not been removed so be sure there is not a partial cap still in there. If the drain hose is not configured properly that can cause this too. The drain hose should come through the cabinet very high to prevent the sink from backing up in the dishwasher. Regular dish soap residue can cause blockages too. If you see suds in the water in the dishwasher then that is pretty strong evidence that there is regular dish soap residue which could be from pre-soaking dishes before adding them to the dishwasher or from the low drain hose and the dish water backing up into the dishwasher drain hose. The issue also could be related to a blockage in the drain pump or a failure of the drain pump. When there is water that has not drained out from the dishwasher always start a cycle then cancel it and allow the cancel to complete. Do not remove the filter unless there is no water in the dishwasher. If there is debris in the undrained water in the dishwasher then removing the filter may allow the debris to get into the pump and damage the pump or restrict it. When you start a cycle then cancel it and allow the cancel to complete (about 2 minutes) that should drain the water out and allow you to clean the filter out without allowing any debris to get past the filter. Otherwise the issue may be a broken impeller on the drain pump or a failed drain pump that needs replacing.

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