So you've started up your irrigation sytem and your Lawn Sprinkler Valve Won't Turn Off. Now what do you do! Why is it doing that? Here is some insight into what is going on and what you or an irrigation contractor might be able to do about it, at least for the time being until you can get the system repaired.
Before you move on to calling a sprinkler repair service, see if you can turn off the backflow control valve. What you're looking for is a green rectangular box that is about 14" x 18". Inside this box you will usually find your backflow control valve. The backflow control valve prevents back siphonage of hazardous waste into your drinking water (if you don't have one, you should consider having one installed). If you can locate this valve, simply turn the valve to the off position.
Another valve that might be in the vicinity of the water main meter would be an emergency shutoff valve, which is a ball valve style shutoff point to isolate the entire sprinkler system water supply. It is often installed in a circular valve box with a green lid, about 5.5" in diameter. If you have a ball valve, it is likely to be located close to the water meter where the lawn irrigation system taps into the pvc or galvanized piping that is your water main. If you have an emergency shutoff ball valve, simply turn it to the off position. If you do not have a provision such as a ball valve to shut off your irrigation in an emergency or for winterization purposes, you may want to consider having one installed.
A third valve, which is actually the zone valve that is malfunctioning and staying stuck in the "on" position, is your zone valve. These are often located in a round green box or in one rectangular green box in what is called a valve manifold setup. If you can figure out where this valve is located, you can manually work the valve on and off to see if it seats and allows the system to shut down. What is causing your problem is the fact that the valve is either old and faulty or it has debris in it which is not allowing it to seat and seal properly.
After trying all of the above, as a last resort, you can opt to turn off your water main. I say last resort because you want some water pressure to your sprinkler system to see if you can get by without totally shutting down your water supply...don't you? So to turn off the water main, locate your meter then turn the key to the off position.
Tuning up your irrigation for your yard in the spring can help to prevent system failure, particularly to prevent or preemptively diagnose issues where a zone valve that won't turn off. Precautions should be taken in case of such failure, such as the installation of emergency plumbing water main shutoff ballvalve or a back flow preventer (which can be shut off). Lastly, excercise caution when working around pressurized pvc pipes, faulty valves and wires as they may be hazardous.
