Flojet check valve failure

[skids]

First time for using water pump - EVER. Pump was cycling on and off with no water running In faucets or toilet and hot tank full. I could hear water flowing through the pump and into the hose to the FW tank. I hooked-up city water and turned the power off to the pump and eventually water was flowing out of the overflow outside. Irritating. This unit has only had RV antifreeze in it as far as I know (bought it new). I checked into buying a check valve assembly for the pump and it was about $20.00 + shipping. A new pump is $61.00 if I just replace it. I may tear into the pump tomorrow to see if the diaphragms were not installed properly or if some debris is preventing proper operation. DAMN we are finally going camping on Monday...