How to replace the sprinkler valve guts:
Before going through the effort of replacing the guts, it might be worth doing a check of the solenoid itself. Usually they fail electrically (short or open) so the timer can’t control it. If you have multiple valves, you can try turning off the water and swapping the solenoid with one from a different (working) valve to see if the problem ‘follows’ the solenoid. Note that you need to turn off the water before removing the solenoid or you’ll have water going everywhere 🙂
If the solenoid seems good and the above steps suggest the valve is bad, you can usually replace/repair the valve yourself. Usually they can be fixed by replacing just the guts of the valve and you can avoid buying a complete valve and having to cut pipes to install the new one.
To replace just the guts yourself you’ll have to turn the water off. If you can’t turn off just the irrigation water, you can turn the water off to the whole house. Look for valves on the side of the house, or the main water line valve that’s typically located close to the street. To avoid having the water off while you get parts, I recommend just taking a photo of the valve to an irrigation supply store (typically not a big box store like Home Depot/Lowes) and ask them to sell you the “guts”. If you can’t find just the guts, try to buy the exact same valve and take the guts out of it. The guts typically consist of rubber parts like a diaphragm, washers and sometimes a spring or two.
Once you have replacement parts ready, remove the many screws around the top of the valve and carefully lift the top off. Pay careful attention where the spring and other parts are located as you take it apart. Gently lift out the guts and then swap them out with the replacement parts and re-assemble it. Re-attach the solenoid on the top if you removed it earlier; don’t make it too loose or too tight; just snug.
Usually this fixes the problem without having to replace the entire valve which often requires digging and cutting pipes to install it…
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