I can’t hear the pump running. We moved this washing machine to this current position 2 and a half years ago and plumbed it in. I think it is syphoning, but why now?
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A discharge hose can over a period of time work its way down into a waste pipe as there is a pulsing motion once the water has discharged, a U trap should be fitted to the hose if it goes into its own waste pipe. If the discharge Hose is attached to the waste of a sink unit, a U trap should be fitted that takes the discharge hose above the water level in the sink.
Hope this helps