Question
I had to shut off the main water supply to the house. when i reopened it, water started flowing from the top of the sprinkler backflow preventer. System was functioning well before. What do i need to do to resume water  supply to the sprinkler system? Thank you.

Answer
Hey Alex, the backflow preventer has a poppet in it that pops to the top of the backflow preventer when you turn the water on, and should seat with the water pressure on. If the water keeps flowing out of the top of the backflow preventer, then either the seat on the poppet has gotten rotten and will no long seat right, or there is something in it that is preventing it from seating right. First try turning the water on and off to see if you can get it to seat right. If that doesn't work, then you will need to take the backflow preventer apart, and either replace the poppet or clean it out. Good luck and have a great day.