[Carl n Susan]

I believe Charlie (the OP) has a 2006 3400RL. Ain't no current type convenience center. in that beast You fill the water tank through the hose fitting at the rear of the RV not by turning the "Fill" switch.

I seem to remember a check valve in the city water input fitting. They have a tendency to stick?

P.S. Charlie - add your year and model to your signature and it will eliminate some of the incorrect responses you receive.