Question
Valve seems to be opening OK, but it is leaking around the anti siphon port lid.  The gaskets seem good and the lid is tight and the unit is almost brand new.

Answer
Hey John, I hope this helps. Inside the lid of the anti siphon port, there is a plunger. This plunger is forced to the top of the lid, and seats at the top of the lid. It could be either that this plunger has gone bad or is deformed, or there is not enough pressure to force it to the top, and allow it to seat properly. That lid will unscrew, and you can access the plunger to inspect it. Good luck and let me know if I can be of further assistance. Thanks and have a great day.