Steve, for the record and trying not to bore with the obvious, the two positions for the valve on my ‘07 Contessa are “City Water - Closed” at 12:00 and “Fresh Water Fill - Open” at 9:00. Incoming water is directed to the tank if set to the later. If disconected from shore water, pump runs from tank. If connected to shore water, pump doesn’t activate if its switch is on and faucet is opened when valve is set to City Water. If hooked to city water and valve is set to Fresh Water Fill, pump comes on, which makes sense as no pressure coming from city water line when valve is closed. Of course tank is filling so this wouldn’t be a long term state.
All this is to say that it’s all about pressure at the pump and in support of the bad check valve theory.
-Will