First, turn off the water! If valves are set incorrectly, you could be over-filling the water tank. The overflow vent would most likely be smaller than the volume of water being forced into the tank. This could cause the tank to expand and perhaps damage structure around the tank.
If your RV has only one way to hook up water, a female hose connector, most likely a valve has to be set. Usual choices are 'Fill' and 'City' but yours might be different. Fill is to be used to add water to the tank and should be monitored at all times. Set the valve to 'City' and now the hose should pressurize the water system and the pump can be turned off. Don't leave the RV with the city water turned on, floods can happen. If you have a gravity fill port for filling the water tank and a separate female hose connector for city water, then you don't have a valve to set.
Not sure about the 3 valves you're talking about, often valves are installed to divert flow from the water heater so it can be drained. You'll have to figure out which water line goes to the water heater, which one is the hot water out line, and a line that might go between the cold in and hot out. If that's the case, the cold in valve should be set 'Open,' the hot out valve shoud be 'Open.' The valve in the line connecting the hot and cold, a by-pass, should be set 'Closed' to make the water go through the water heater.
Note that this assumes the valves are in the water line runs. Valves that are set in 'T' fittings might just divert water and not shut if off. Most valves have a handle that signals condition. If turned parallel to the line, they are open, if they appear at 90º to the line, they are closed.
In the photo below, all 3 valves are set 'Open.' To set for summer use, the valve connecting the blue and red lines should be 'Closed.' to make water go through the water heater.
For winterizing this set up, the valves in the tank in and out lines would be set closed and the center blue/red valve would be open to allow water to by-pass the water heater.
Linear Mode
