Sounds as though there is a water leak somewhere in the system, or the backflow check valve at the pump is not holding pressure. Of course, the switch on the pump could be stuck in the ON position. Or the pump impeller is worn and not building adequate pressure to shut the unit off. I found ours to have a crack around the threaded area of the inlet strainer thus letting in air. This was deemed due to poor winterization or overtightening of the strainer bulb.
Just replace the thing. It will cost less than $100 and is easy to do yourself.
Linda & Bob
Sparta, TN
