I am not super sure that is what it is. The hissing was just the water that was flowing out of the backflow hitting the weather cover. I had this same issue when I first installed the system with the water flowing backwards, but it went away on its own once I got more of the system hooked up so I didnt give it a second thought.
I have a 3/4 T value that goes into a Febco 3/4 backflow preventor that then goes to into four 1" rainbird valves. Ran it last year with no issues. This winter my neighbor told me the winter box was making a hissing noise. I took the cover off and the water was coming out of the bottom of the backflow. So I turned off the T valve and opened all the valves manually to release any pressure in the lines. I left them open. I went out this afternoon to turn the valves off and turn the timer back on a...
I had a similar issue when I installed my system. Make sure the water is turned on at the master valvue...then go to the kitchen sink and unscrew the faucet head and turn the water on. I had dirt in my lines. I slowly let it leak out until it was back to full pressure. Also had to go to the toilets and in the back of the toilet pull the tube that puts new water into the bowl out so it does not refill the bowl but refills the back. I saw dirt and other particles in the water. Flushed about 5 time...
