City Water is filling/overflowing my freshwater tank

wnjj wrote:
The check valve is part of the water pump itself. Try running some water through your system by using the pump. That may reseat it or let whatever debris through that may be making it leak. If that doesn’t work, it’s fairly simple to take the pump head apart to clean and inspect the diaphragm.

If you are referring to the city check valve at the hose connection that is not the issue. That one prevents pump pressure from pushing water out of that connection when it’s not In use,