· by Michael Blair, Nashville's Irrigation
The controller says the cycle ended an hour ago, but one zone is still spraying. Or every zone shuts off on time and one head at the bottom of the yard keeps bubbling long afterward, leaving a patch that never dries. Both tend to show up on the water bill before anyone spots them in the yard, especially on a system that runs before dawn. They have different causes and different fixes, and a few minutes of watching tells you which one you are dealing with.
Stop the water first
A properly built system has its own shutoff between the water supply and the valves, usually a ball valve near the backflow preventer or in a box close to the tap. Close it and the running zone stops without cutting water to the house. If there is no separate irrigation shutoff, the main valve at the meter or where the line enters the house will do, and adding a dedicated one is worth doing during the repair.
Before touching anything else, note what you saw. Which zone was running, whether the controller showed it on or off, and whether water was coming from every head on that zone at full pressure or just trickling from one or two low ones. That covers most of the diagnosis.
When the whole zone keeps running
If the controller is off and the zone runs at full pressure anyway, the valve is stuck open. Each zone valve is opened by a small solenoid that bleeds water off the top of a rubber diaphragm; when the solenoid closes, line pressure pushes the diaphragm down and shuts the valve. A grain of sand or a sliver of pipe from an old repair lodged under the diaphragm, a torn diaphragm or a stuck solenoid will all hold it open. So will a manual bleed screw someone loosened to test the zone and never tightened.
If the zone is running because the controller is calling for it, the problem is upstream: a manual run never cancelled, two programs with overlapping start times, or a failed station output that sends power to that zone constantly. Unplugging the controller, or lifting that zone’s wire off its terminal, settles it. If the zone stops, look at the controller; if it keeps going, it is the valve.
- Controller off, zone still running at full pressure: the valve is stuck open
- Zone stops when its wire is disconnected: the controller or its program
- Zone shuts off but one low head keeps draining: low-head drainage
- Water welling up with no zone running: a leak on the supply side
When one low head keeps draining
A head that dribbles for a while after its zone shuts off is usually not a valve problem at all. When a zone stops, the water left in the lateral pipe runs downhill and out of the lowest head until the pipe is empty. On a sloped lot, and Brentwood, Franklin and the hills west of town are full of them, that can be a real volume of water every cycle, and it keeps the bottom of the yard boggy.
The fix is a check valve at the low heads, either built into the head body or added as a fitting beneath it, which holds water in the line until pressure opens it again. If a low head dribbles constantly, not just after a cycle, the valve upstream is weeping: closed but not sealing, with a small steady flow past a worn diaphragm or a bit of grit.
Fix it before the winter blowout
A valve that is not sealing should be repaired before the system is winterized, not left until spring. When the lines are blown out with compressed air, a leaking valve lets water seep back into them, and a line holding water through a hard freeze is the one that splits. Rebuilding a valve usually means a new diaphragm and a cleaned bonnet, a small job when the valve sits in a box someone can reach.
Around here, reaching it is often the hard part. Valve boxes that have sunk, filled with clay or been sodded over are common, and finding them can take longer than the repair. Once the valve is fixed, it is a good time to raise the box, clear it out and mark it on a sketch of the yard, so nobody has to probe for it next time.