Water pump or owner malfunction - Update

avan wrote:
..snip.. So I did the normal water fill - hooked up the hose with pressure regulator to the screw on water fill, switch the lever that's there from "normal operation" to "water fill" and proceeded to take on a full tank of water. Have done this hundreds of times and this was no different. Switched the lever back to 'normal' and disconnected the water and pressed the plug back into the water fill opening. ..snip..

I think it is that valve (the one with the lever on it that you turn to change where the water goes) that is bad. It is letting the pump push back into the FW tank. At least that is how mine works - if I forget to turn the valve back into normal position after filling the tank the pump will run and run because it never builds up pressure.