There are a few older valve models that don't warrant rebuilding. When you see these models, save your time and effort and immediately start working to cut out and replace. I won't give you a list of the models that we have problems with, as it may seem to be disparaging to those manufacturers, and mostly it's just old models that are out of production. Instead, if you're working as a technician, pay attention to the patterns and make your own list. There's no shame in cutting a valve out and replacing it with a new reliable model, instead of rebuilding the valve two or three times and still being unsure of it's reliability going forward.
If you've gone through your troubleshooting sequence, and have determined that the solenoid is bad, just replace it. Turn off the main water supply first, though. Some valves are ok to replace the solenoid with pressure on them, and some are not. It's easy to cross-thread the solenoid when there's some pressure shooting out the small hole in the solenoid attachment pit.
When you've worked through the troubleshooting methodology and determined that the diaphragm isn't working correctly, I recommend a total rebuild, meaning everything that can be removed off the lower valve body is removed and replaced. It's quite possible to just replace the problem component (usually the diaghragm) and return the valve to service, but years of experience has shown the error of that thinking. It's generally cheaper to buy an entire valve than to purchase the components separately, and with the cost of most valves being very reasonable, there's no reason not to replace everything. While you have the valve dug up and opened up, why not replace everything you can? If you're a contractor that warranties your work, you will be held responsible for the performance of that valve into the near future, so why risk a call back by not replacing all the components of the valve?
Water Leaking From Sprinkler
This is an issue that we get calls for often. Your first question has to be, “Is it leaking all the time or just when the zone is running?” If the leak is only occurring while the head / zone is running, then a simple head replacement is called for. Water leaking constantly from a sprinkler normally indicates two things. The first is that the leaking head is the lowest in elevation on that zone, and the second is that it's the valve that's leaking, not the sprinkler. A valve will sometimes get a particle lodged between the diaphragm and it's seat, or the diaphragm itself will become damaged. A small amount of water leaking through will flow to the lowest head in the zone and start to dribble out. This is assuming that the head doesn't have a check valve. I've seen other contractors try to address the problem by putting a check valve on the lowest head. Guess what, the water just backs up to the next lowest head and leaks from it. I suppose that if all the heads had check valves, then possibly none of them would leak unless the pressure built up past the threshold limit (usually 8-10 psi.) Regardless, it's the valve that needs to be addressed not the heads, see “Single Valve Stuck On” step 3.
Single Zone Isn't Operating
1) First, ask enough questions of the homeowner or property manager. How long has this been going on? Has the system been used often or has it been off for the winter or possibly years? Has there been any construction or work of any kind happening on the property, especially cable / utility work? Has there been any new plants installed recently or new bed edges dug? Make sure the other zones are working and that water is flowing normally into the system.
2) Troubleshoot the timer settings first. Run through a quick check of ALL the settings, and make sure there's Run Time set for that zone. Turn the zone on. Walk the property and look for any leaks that may be occurring, look and listen! Give it a few minutes to see if any water comes to the surface, during this time, try to determine where the valve is, and walk the suspected pipe path between the water source and the valve, then out into the zone itself.
3) Go back to the timer. With the zone still on, use your multi-meter to measure the voltage on that circuit and then check the rest of the circuits. If you get voltage on any of the other circuits, there can be two problems happening. Either the timer has a problem or there's wires touching in the field or otherwise allowing voltage to be fed back through the other zone wires.
To determine if it's the timer, mark the wiring diagram or take a picture of the terminal strip with your phone to make sure you put back all the wires correctly. Turn the timer to the OFF position, then remove all the wires. Manually run that zone again and recheck the voltage on that zone then all the others. If you're still getting voltage across more than one zone, you've got a bad timer. If not, there's wiring problems. The wiring bundle may have been cut through with a shovel and the wires are still close enough so that electricity is jumping the gap enough to be measured at the timer, or maybe a valve box is filled with water and all the wire connections are exposed or not protected by grease filled wire nuts. This can cause electricity to feed back along other wires.
Assuming all the voltage checks are ok, now turn OFF the timer, insure that there's no current flowing, then check the resistance of the circuit with the Ohms setting on your multimeter. Also check the other zone circuits at this time to get an idea of what is normal from the other operational zone circuits. It helps to know what kind of valves you're dealing with so that you can know how many Ohms to expect from a healthy solenoid. Remember that the circuit will show the resistance of the solenoid plus the wire circuit plus one Ohm or two at most for the circuit inside the timer. If you get abnormal resistance readings, disconnect the wires for that circuit, check the resistance across the timer terminals, then measure the Ohms across the two disconnected wires. If the Ohms are too low, there's either a short in the wiring or in the solenoid. If the Ohms are too high but not infinite, it may be the solenoid going bad, or it might be a corroding wire splice at the solenoid or somewhere in between. If the Ohms are infinite (pegged out high) then the solenoid could be bad or the wire circuit is open somewhere, check the wire connections at the solenoid.
4) Reconnect all the wires if necessary then start that zone again with the timer. Now go to the valve. Do an eyeball check of the valve, is there a leak, was the valve installed correctly? If the valve or system was just installed, there may be some glue covering the pilot tube opening inside the valve under the solenoid. Try to actuate the valve by opening the bleed screw or by partially unscrewing the solenoid. If the valve won't come on, you've got a mechanical problem with the valve itself, probably the diaphragm. Rebuild the valve, or replace if necessary. If the valve did turn on when using the bleed screw, continue to check the solenoid. Are we receiving voltage to the solenoid? You can use the multi-meter to check the voltage at the wire splices. If unsure, turn the timer off then disconnect the wire splices. Restart the timer on that zone, go back to the valve location, and check the voltage at the disconnected zone wires. If that looks good, now we need to determine if the solenoid is operating properly. I recommend using a Station Master to apply voltage to the solenoid. If the solenoid doesn't actuate then replace the solenoid, wire it back up, and recheck operation from the timer.
5) If the valve was coming on when checking it manually, and the solenoid and electrical circuit checked out good, we've got a more complex problem. You should be able to hear or feel water passing through the valve if it's running normally. Recheck for a leak somewhere. Then, check for obstructions in the piping system. This is a factor that can't easily be tested for, it has be eliminated down to. If all the other possibilities have been eliminated, get out your garden hose. Unscrew a head and use an adapter to connect a garden hose. Turn on the water and back-pressure the zone. You may have to take off another head or disassemble the valve to be able to properly flush out the obstruction.
Single Zone Stuck On
1) Remember to ask questions; has there been any work done in the area? Has anyone else, such as a cable contractor, pool installer, or landscaper performed any repairs to the system? Look around yourself. Occasionally, when construction work has happened and pipes cut through, a zone pipe will accidently be plumbed directly into the main line. That's a pretty rare occurance, but it's happened a few times to my clients.
2) Check the timer first. Is the timer running? There may be errant settings that make it appear that the zone is stuck on, but it's actually the timer that's keeping the zone on. If the timer is running zone visibly, as in you can see on the screen the icon for system running and see time counting on that zone. Now get out your multi-meter and check to see if there's any voltage on that zone's terminals. It's possible that a circuit failure in the timer is causing the zone to run.
3) In the absence of timer or electrical issues, we know the problem is physical/mechanical. Address the valve. Take the valve apart and check the diaphragm for tears or a warped / distended appearance. Look inside the lower valve body, and stick a finger down into the hole to check for pebbles, debris, or even shards of broken PVC. You may need to turn the valve on for a couple seconds to fluch out anything in the pipes. Since you have the valve taken apart, I would go ahead and rebuild the valve if possible. If it's not a model that you would rebuild, then reassemble and see what happens. You may need to replace the valve.
Single Zone Has Weak Pressure
1) Generally, this is caused by physical or mechanical issues. Always walk the yard to insure that you're not missing a pipe break or damaged head. Look closely, a missing sprinkler may not be shooting into the air, it may just be barely bubbling while it leaks a ton of water. Be sure to check around the entire property, there may be a sprinkler or drip line in a very improbable place that's attached to this zone. Check the water meter to see if it's turning slowly or as fast as a normally operating zone.
2) Check flow demand of the zone. Ask the customer if any recent repairs or additions have been made to the irrigation system, particularly the zone in question. It's possible that an additional sprinkler or two has been added to the zone, exceeding the flow / velocity limits of the zone piping. It's not uncommon to find that larger nozzles were put on to cover an expansion of flower beds or turf area. It's also possible that cable construction, landscape installation, or something similar has hit a pipe and crimped or crushed it without breaking the pipe. Like I said before, ask plenty of questions, and look for evidence of recent work on the property.
3) Locate the valve, troubleshoot the electrical side of operations, if not electrical, then disassemble and look for obstructions. Rebuild or replace the valve.
4) If the problem persists, remove a head and recheck pressure. It's possible that a zone line was broken by a cable contractor, or maybe even a main water line break upstream of the property, and rocks, dirt, or debris pushed into the irrigation system . If so, they normally accumulate at the barbed elbow or in the sprinkler head.