When one zone fails and every other zone still runs, the fault is almost always in something that zone does not share with the others: its valve, its solenoid, its station wire, or the controller output driving it. Anything shared — the water supply, the transformer, the common wire — would have taken down more than one zone. That single observation eliminates most of the system before anyone opens a valve box.
Why one zone is easier to diagnose than several
An irrigation system is mostly shared infrastructure. One supply, one mainline, one controller, one transformer, one common wire running to every valve. Each zone has only four things of its own: a valve, the solenoid on it, the station wire running from the controller to that solenoid, and the station output inside the controller.
So a single dead zone is a gift, diagnostically. Water is clearly reaching the manifold, because the neighbouring zones run. The controller clearly has power. The common wire is clearly intact. Whatever is wrong is in one of four components, and all four can be checked in under an hour.
The four candidates, in the order they are checked
That last test is the fastest single diagnostic on the whole system, and it is why a technician usually goes to the valve box early. Bleeding the valve open by hand separates "the valve will not open" from "the valve is never being told to open", and those have completely different repairs.
- The controller output. A technician measures for roughly 24 volts AC between that station terminal and the common while the zone is called. No voltage there and the fault is inside the controller — a failed station output, a blown fuse, or a triac failure — and nothing outside needs touching.
- The station wire. With voltage confirmed at the terminal, resistance across the station and common wires tells you about the field. An open circuit means a broken wire or a failed splice between the controller and the valve. A short means damaged insulation somewhere along the run.
- The solenoid. A healthy irrigation solenoid reads within a normal resistance band. An open reading means the coil has burned out; a very low reading means it has shorted. Both are inexpensive parts.
- The valve. If voltage arrives and the solenoid is good, the fault is mechanical. A stiff or torn diaphragm, debris on the seat, a stuck plunger, or a flow control stem closed down. Manually opening the valve with its bleed screw settles it immediately: if the zone runs when bled by hand, the hydraulics are fine and the problem is electrical.
What the symptom pattern tells you
| What you observe | Likely cause |
|---|---|
| One zone dead, all others normal | Solenoid, valve, station wire or station output |
| One zone dead and the controller shows a fault or error | Short on that station — wire or solenoid |
| Zone runs when the valve is bled by hand | Electrical — no voltage reaching the solenoid |
| Zone will not run even when bled by hand | Water is not reaching that valve, or the valve is mechanically stuck |
| Zone works intermittently, worse after rain | Compromised wire insulation or a failed splice in a wet box |
| Zone failed after recent digging | Cut station wire or punctured lateral |
| Several zones dead, not one | Common wire, transformer, fuse or supply — a different problem |
Want this looked at rather than read about?
Diagnostic-first visits across North Georgia. Call 770.335.8595 or request service — you get an estimate before any work begins.
The two things a homeowner can usefully check
First, confirm the program is actually calling the zone. It sounds trivial, but a zone excluded from the active program, a run time set to zero, a seasonal adjustment at zero percent, or a rain sensor holding the system off all look exactly like a dead zone. Start the zone manually from the controller rather than waiting on the schedule — if it runs manually, nothing is broken and the fix is in the program.
Second, note whether anything was dug in the past couple of months. Landscaping, fencing, a mailbox post, aeration, a utility trench. Wire damage frequently takes weeks to surface, because a nicked wire keeps conducting until moisture reaches the copper, so the work that caused it is often further back than people think to mention.
Beyond that, do not open the controller. The measurements above involve live 24-volt circuits and a meter, and the value is in interpreting the readings rather than taking them.
What the repair usually involves
On the majority of single-zone calls the answer is a solenoid or a valve rebuild, both of which are done by lifting the valve box lid with no excavation, and both of which are inexpensive parts. A failed splice in a wet valve box is next most common, and it gets redone with a direct-burial gel-filled connector rather than the tape or indoor wire nut that failed.
A genuine wire break out in the field is the least common and the most time-consuming, because the break has to be located before it can be repaired. An inductive locator puts a signal on the wire at the controller and follows it until the signal stops, which converts a property-wide search into one targeted hole.
Irrigation Medics bills $125 for the first hour on site and $80 per hour after, with parts separate and an estimate before work begins. Most single-zone faults are found and fixed inside the first hour.
Related answers
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Services that fix this
Sprinkler Zone Repair
One zone dead while the rest run fine — the most common irrigation call there is, and the most diagnosable.
Read more →Irrigation Valve Repair
The component that decides whether a zone runs at all — diagnosed, rebuilt or replaced.
Read more →Irrigation Electrical Repair
Cut wires, shorts, blown fuses and corroded splices — traced to the break instead of guessed at.
Read more →Where we work
Irrigation Medics repairs irrigation systems across Hall County and the Lake Lanier communities, the Gwinnett corridor through Duluth, Suwanee and Buford, and North Fulton and Forsyth — Johns Creek, Alpharetta, Milton, Roswell and Cumming. Same rates throughout. See the service area.