Can a broken circulation impeller cause a dishwasher not to drain?

Question

Problem

I have a Maytag dishwasher (model MDB4100AWW, serial number starting with 12) that does not drain. During the wash and rinse cycles, water enters the dishwasher and sprays. But during the time when it should drain, the dishwasher makes a buzzing sound, but no water drains.

I disassembled it from inside the washer and found that the circulation impeller was broken. The bottom plate of the circulation impeller had separated from the rest of it. The top and blades were still attached, which I guess is why water continues to spray. Here's a photo:

Indeed, after removing the broken circulation impeller, the dishwasher fills but water does not spray, which makes sense.

I will replace the circulation impeller soon, but I don't know if this is the only problem.

See a parts diagram for this dishwasher. My broken impeller is number 14 in that diagram, part 99002069. A separate part is the drain impeller (number 22 in the diagram, part 903304), which I checked and found to be intact.

Things I've tried

• Disassembled and cleaned interior washing mechanism; found no problems except broken impeller
• Verified that the air gap hose is clear
• Ran dishwasher with and without broken circulation impeller
• (UPDATE) Removed drain cover and found that the drain impeller looks fine

Things I still need to try

• (UPDATE) Replace the broken circulation impeller (hopefully Friday 01-29)
• (UPDATE) Install a check ball (week of 02-01). When I removed the drain cover, I found that the check ball was gone. I read on the Interwebz that the check ball can dissolve over many years and go down the drain when it's small enough. I don't know if that's credible, but nevertheless, it's gone, so I ordered a new one that will arrive next week.

Question

Does the circulation impeller have anything to do with draining? Could this broken impeller possibly be the only reason the dishwasher doesn't drain?

Answer 1

The impeller is the main part of the pump. The pump makes the water spray and it also pumps the water out after the wash or rinse cycle has finished. Usually the drain solenoid opens and since the pump is running all the water goes out the drain instead of through the sprayers.

It doesn't drain by gravity since it pumps up to the sink tailpiece or other entry to the plumbing drain system.

Once you repair the pump all should work as normal but you will have to drain it by hand before repairing it or dump the water all over under it when you open it back up.

Note: some dishwashers have two impellers: one to spray the water during the wash cycle, and one to drain the water. Replacing the spray impeller will not fix drainage problems. If your drain impeller is fine, either your drain line is blocked, or your motor has problems.

Good luck with your project!