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BAD CHECK VALVE!!

It was not immediately apparent why the pump would run forever and not pump the water up. Some suggested drilling weep holes that just enabled water to pump underneath the check valve. It wasn’t until I finally took apart the plumbing that I discovered the check valve was just a round disk flap that I believe was connected originally on one side by the rubber o-ring / gasket, and it ultimately ripped off its gasket. The result was a disc inside the check valve that would probably rarely ever work correctly as a check valve, but commonly get pushed by the pumped water up against the other side of the check valve, effectively making it work like a check valve in the opposite direction. This would not happen all the time, and typically just shutting the pump off for a second would enable it to pump the water out. It was a heck of a conundrum for several weeks or months until I took apart the check valve and replaced it.