Hello, I just had an irrigation system installed and like it alot. but, one of the heads stays up after the zone runs. I had Hunter I20's installed. I noticed that while it's running that water runs out between the part that pops up and the "nut" that screws on to the entire head. Then when the zone is done, the head doesn't return done. I unscrewed the "nut" and took out the head and rinsed it out, but still doesn't retract. Can anyone assist me? Thanks so much.