StarkNaked wrote:
Your check valve has failed, or is stuck. It could be as simple as re-seating the check valve.
Here are the instructions to fix.
https://www.sunlineclub.com/forums/f71/fresh-water-inlet-valve-repair-11736.html
Helpful hint: Never push the check valve in when the systems is pressurized, even just a little bit of water pressure.
If you can't fix right away, all you need is a male garden hose plug. Just screw it in where you would put your hose and it will seal the pressure.
That is your problem and resolution
If the O-ring on the check valve plunger has become dislodged...replacement needed to fix it
OR install a brass garden hose shut off and forget about it
**Closed when using pump----Opened when connecting to city water via hose