My irrigation system (which is one year old) recently began leaking through one of the sprinkler heads (the bottom-most sprinkler head). I traced the problem back to the solenoid valve. It is not sealing completely. I know this because I hear a faint hissing sound at the solenoid. When I cut the water at the source, the hissing and leak stop.
I had a professional reinstall the solenoid cylinder as well as the top part of the base (diaphragm part). The bottom part of the base, which is connected to the pipes, is still the original. After doing this, the leak and hissing stopped for one day. But now it's back. No hissing, but a constant drip leak through the sprinkler head.
I guess the next step is to cut the pipe and reinstall the base of the solenoid kit. But I'm wondering if there is another solution. The solenoid kit was not installer perfectly level. The inflow pipe is about a 1/4" lower than the outflow pipe. Could this be causing the problem? I'm pretty sure gravity plays a big part in how the solenoid works. So I'm thinking if I dig and level out the pipes and solenoid kit, that might fix the problem. Is this worth it? Does the solenoid have to be near perfect level for it to work properly?