What are some common causes of a dishwasher that won't drain?

The causes of dishwasher problems can vary by manufacturer and model, but blockages of the filter or waste pipe cause most drainage problems, according to Dr. DishWasher. If there are no blockages, the most likely problem is a defective drain pump.

Filter blockages require removing the lower basket and filter from the bottom of the dishwasher and cleaning with soapy water. The process for removing waste-pipe blockages involves disconnecting the pipe from the plumbing under the sink and removing any objects that are blocking the pipe.

Defective drain pumps either don’t run or make an unusual noise during the drain cycle. It is best to contact a dishwasher repairman to replace a defective drain pump.