Fresh Water Pump

My Safari has a valve in the Wet Bay that must be open to fill the fresh water tank
And closed to use shore water or the pump

RV Water pumps use a diaphragm as a check valve.

You can disassemble pump and clean up check valve (typically being held open due to hard water deposits)......replace check valve
OR
Install a 1/2" in-line check valve in suction line to pump (simplest fix)

Suction side......
Reason is if on discharge side of pump the pump check valve will still allow leakage back thru pump (just the pump portion cause new check valve will hold system line pressure) When pump pressure drops pressure switch will turn pump on the shut it off Pump will short cycle frequently which is not good for pump and will irritate you do to the constant ...burrrrup...of pump

Thank you Toddupton.

Depends on the pump. You can try pulling the valve out and cleaning it

So do I need to replace the pump or is there an easy way to replace the check valve.

Bad check valve in your water pump