This is a pretty common problem and the solution is blindingly simple. It’s caused by the drain hose siphoning water out of the washer tub. There are two common causes for siphoning and I’ll explain both of them below.
One cause for siphoning is simply that the drain hose discharge is below the fill level of the washer tub. This picture shows the minimum drain height needed to avoid siphoning.
Another common cause for siphoning is not having an air break between the drain hose and the drain stand pipe. Usually, this isn’t a problem since the drain hose diameter is usually much smaller than the diameter of the drain stand pipe. But sometimes folks will inadvertently remove the air break by duct taping the drain hose to the stand pipe. They might do this because the drain hose keeps popping out of the stand pipe when the washer pumps out the tub. Other times, the drain hose might fit into the stand pipe with a tight interference fit.
The other day, I talked to a guy on Skype who was having this problem with his washer. Since he didn’t know what caused it, he had taken is whole washer apart, thinking there was something wrong with the pump! I thought I could hear him kicking himself after I explained this siphoning business to him!
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