Unwinterize problem

[Richard]

I have a 2016 Jayco North Point 301 RETS. I unwinterized it today. All lines are flushed out and running clear. The hot water heater is full and the air is pushed out. I have all of the valves pointed in the right direction for "City Water". When I turn on the city water, the water is available at the faucets in the trailer but water is flowing into the fresh water tank too. Any ideas on why the fresh water tank is filling up?
Thanks
Richard

[Racinforthefinish]

There is a back flow preventer in your water pump that must be stuck open. Sometimes tapping on it will work or you may have to work on it. Someone else will chime in with more details on technicalities.