There is a recirculation valve inside the pump that stops the pump locking up when you release the trigger. This is probably dirty and / or sticking.
With a modicum of common sense and the ability to think things through, it is possible to discmanthe the pump, work ot where the valve is and how it works and clean it out.
You MAY be able to locate an exploded diagram fo ryour washer or one similar using Google image search
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March 2016