Make sure both levers (ball valves) are open. Your PVB will leak water from under the bonnet and then will seal itself with the water pressure once the levers are fully opened. If it continues to leak with the valves wide open, you have an internal issue with your PVB. Just another heads up, I am not sure of your climate, but when you winterize your system in the fall, it is a good idea to leave your levers (valves) in a 45 degree position to keep the ball valve from freezing, expanding, and cracking.
Tony Posey
Ridge Run Landscapes