· by Michael Blair, Nashville's Irrigation
Every other zone comes on when it should. One does not, and the grass in that part of the yard is showing it. Because the controller, the water supply and the backflow preventer are shared, a single dead zone rules them out; the problem is somewhere between the controller terminal for that zone and the sprinkler heads it feeds. That is a short list: the wire, the solenoid on the valve, the valve itself, or something blocking the valve. The order to check them in goes from cheapest to most work.
Start at the controller
Run the zone manually from the controller and listen at the valve box, if you know where it is, for a click as the solenoid pulls in. No click and no water means the valve is not getting power or the solenoid is dead. A click with no water means the solenoid works and the valve is not opening.
Inside the controller, check that the zone wire is seated in its terminal and that the common wire is tight. A multimeter across the zone terminal and the common, with the zone running, should read the controller’s output voltage, usually around 24 volts AC. No voltage means the controller output for that zone has failed, which on some units is fixable by moving the wire to a spare terminal and reassigning the zone.
The wire
If the controller is putting out voltage, the wire between it and the valve is next. With the controller off, measure resistance between the zone wire and the common at the controller. An open reading means a break in the wire or a bad splice; a very low reading means a short. Wires run underground in the yard and get cut by edgers, by planting, by fence posts and by the occasional excavation, and old splices that were not waterproof corrode.
Finding a break in a buried wire is done with a wire tracer, which a technician will have, or by checking the splices in the valve box first, since those are the usual failure. A new wire can often be pulled alongside the old run, or a spare conductor in the same cable used, rather than digging up the whole path.
- No click, no voltage at the terminal: controller output
- No click, voltage present: wire or solenoid
- Click, no water: valve stuck, diaphragm or debris
- Weak flow only: partly open valve or a broken lateral
The solenoid and the valve
The solenoid is the small cylinder on top of the valve with two wires. Measure across its wires: a reading in the tens of ohms is normal; an open reading means it has failed, and it unscrews and replaces in a minute. If the solenoid tests good and clicks, turn it a quarter turn by hand to open the valve manually. Water flowing means the valve works mechanically and the problem is electrical after all; no water means the valve is stuck.
Valves stick when debris lodges in the diaphragm or the small ports that control it, or when the diaphragm has torn. Turn off the water, open the valve body, rinse the diaphragm and the ports, check the small filter screen, and reassemble. A torn diaphragm is a rebuild kit. Zones fed from a well or after a main break are the ones that get grit in the valve.
When the zone is weak rather than dead
A zone that comes on but barely sprays, with heads that rise partway and dribble, has a different problem: water is escaping before it reaches the heads. Walk the zone while it runs and look for a wet spot, a sinkhole or a fountain, which is a broken lateral pipe, usually from a shovel or a root. If nothing shows, the valve may be only partly opening, which points back to the diaphragm, or the flow control on top of the valve has been turned down.
Diagnosis at this level is what an irrigation technician does in the first half hour of a service call, and having done the controller checks yourself narrows what you are paying them to find. A zone that dies every spring at startup, though, is usually a splice or a wire that has been failing for years, and it is worth having the run replaced properly rather than repaired again.