I noticed that the valve box in the back of the house, along with the area around it, is occasionally flooded with a significant pool of standing water. The frustrating part is that I could run the system every day for a week with no flooding and then run it on the eighth day and it floods. When this occurs I go to my water meter and verify that water is in fact running. I than shut the main water supply to the sprinklers off for a day or so. I than turn the main water supply back on the following day and run the sprinkler again for a few days with no flooding. It is very non-repeatable and difficult to recreate.

Since there are four zones controlled in the valve box, I�ve run each zone individually (rather than sequentially running all four zones) and after much trial and error was able to determine the problematic zone that causes the leak.

I believe when I had the system installed five years ago, the contractor used RainBird heads and valves. My question is what is the probable cause of the leak and how do I fix it?