A stuck valve, open manual bleed, or bad controller relay keeps sprinklers running; shut water at the backflow, then test valve and wiring.
Your lawn is getting drenched, the water meter is spinning, and one or more zones refuse to quit. This guide walks you through fast shutoff steps, smart tests to isolate the fault, and field-proven fixes. You’ll see how to tell a valve problem from a controller issue, what debris does inside a diaphragm, and where to turn the water off without taking down the whole house. Two quick data tables keep the plan tight and skimmable.
When Your Lawn Sprinkler Stays On — Quick Checks
Start with safety and control. You’re stopping water flow first, then finding the cause. Work through these steps in order; each one narrows the problem.
Step 1: Stop The Flow Safely
Find the irrigation shutoff at the backflow device or the system’s main ball valve. Most outdoor backflow devices have two shutoff handles; turn the handles perpendicular to the pipes to stop water to the sprinkler piping while keeping the home supply live. If your system lacks a separate shutoff, close the dedicated irrigation valve wherever it tees off the main. This buys time and prevents pooling while you troubleshoot.
Step 2: Tell If It’s Electrical Or Hydraulic
Unplug or power down the controller. If the zone keeps running with the controller disconnected, the valve is physically stuck open or manually opened. If the flow stops only when the controller is off, the issue points to wiring, a stuck relay, or a programmed schedule.
Step 3: Check For A Manually Opened Valve
Pop the valve box lid. Each zone valve has a small solenoid on top with two wires. Turn the solenoid clockwise until snug to close a manually opened valve. Many valves also have a bleed screw; make sure it’s not cracked open. If the water stops, you found the cause.
Common Causes And Fast Tests
Use the table to match symptoms with likely causes and quick isolating moves before you break out tools.
| Symptom | Likely Cause | Fast Test |
|---|---|---|
| Zone runs with controller unplugged | Debris in valve or torn diaphragm | Shut water, open valve, rinse diaphragm and seat; reassemble and retest |
| All zones stuck on at once | Master valve stuck or main relay shorted | Kill controller power; if still on, service master valve; if off, check controller output |
| One zone only, intermittent | Solenoid sticking or small grit in metering port | Swap solenoid with a known good zone; see if the problem follows |
| Zone never fully shuts; slow weeping | Diaphragm warped or seat nicked | Inspect diaphragm for tears; replace diaphragm/bonnet kit |
| Runs after a repair or new install | Trapped debris from line work | Manual flush: open bleed, flow control mid-open, purge, then reseat |
| Heads run only when another zone runs | Crossed wires or miswired common | Pull the suspect zone wire at controller; verify behavior stops |
Why debris matters: a speck in the metering port or on the seat can hold the diaphragm off just enough to keep water moving. Many manufacturers note debris as the top reason a valve “weeps” or won’t close.
How Irrigation Valves Close
Knowing what’s happening inside the body makes the fix straightforward. A zone valve uses a rubber diaphragm. During normal shutoff, pressure builds above the diaphragm through a tiny passage. That pressure presses the diaphragm against the seat and the flow stops. The solenoid opens a pilot path to drop the pressure above the diaphragm when watering starts. If grit blocks the metering port or the pilot path, the pressure balance never returns and the valve stays open.
Parts You’ll See In The Box
- Solenoid: the small coil with two wires; unscrews by hand.
- Bonnet: the cap you remove to access the diaphragm.
- Diaphragm and spring: the rubber disc and its helper spring.
- Flow control (if equipped): a stem that lets you throttle or close flow during service.
Field-Test Flow: Narrow It Down In Minutes
Use this sequence to zero in on the fault without guessing. Keep the controller off while you test unless a step calls for it.
Confirm Power Isn’t The Driver
Disconnect the zone wire at the controller for the running zone. If the zone keeps running, you’ve ruled out a phantom schedule or wiring call. Focus on the valve. If it stops, investigate programming, stuck relays, or a shorted wire.
Try The Solenoid Swap
Unscrew the solenoid from the stuck zone and swap it with a known good zone’s solenoid. If the problem follows the solenoid, replace it. If not, the body/diaphragm needs attention.
Flush The Valve Body
Shut off water at the backflow, open the valve bonnet, lift out the diaphragm, and rinse any grit from the seat and metering port. Reassemble, turn water on, and test. This single step clears many “won’t shut” cases after line work. Manufacturer guides call debris the most common cause and recommend cleaning the diaphragm and seat.
Use The Flow Control
If the valve has a flow control stem, turn it down to help the diaphragm seal during testing. This can stop seepage while you confirm the fix, then reopen to normal.
Shutoff Points And What Each One Does
Fast shutoff saves plants and water bills. Here’s where to close things and what stays online.
Backflow Shutoff
Most systems include a pressure vacuum breaker or similar device near the supply. Two ball valves flank it. Turn both handles perpendicular to the line to stop flow to irrigation only. This leaves indoor plumbing live.
Zone Valve Box
In the valve box, use the flow control to choke down a single valve or close the manual bleed and solenoid. This targets one zone while others remain available later.
Controller “All Off” Isn’t A Guarantee
If a valve is stuck or manually opened, power commands won’t help. That’s why the unplug-test is so handy: it separates electronics from hydraulics in seconds.
Step-By-Step Repairs That Last
Once water is safe, pick the path that matches your diagnosis. Keep a towel and a small bucket handy. Take photos as you go so reassembly is simple.
Clean And Reseat The Diaphragm
- Cut water at the backflow or system shutoff.
- Mark the valve orientation, then remove bonnet screws.
- Lift the bonnet and diaphragm; note spring placement.
- Rinse the rubber, spring, and seat. Clear the metering port.
- Rebuild in the same order. Hand-tighten evenly.
- Turn water on slowly. Test.
This clears grit and restores a smooth seal on the seat. Manufacturer support pages list this as a first repair move for valves that won’t close.
Replace A Tired Diaphragm
If the rubber is rigid, torn, or cupped, use a diaphragm/bonnet kit for your exact model. Many valves share kits by brand and series. Replace screws and O-rings as supplied.
Swap A Faulty Solenoid
With power off, unscrew the solenoid, match voltage (most residential units are 24 VAC), and wire-nut the new leads to the zone and common. Keep splices waterproof with gel-filled connectors. A bad coil or sticking plunger can hold a valve open.
Fix A Controller-Driven Runaway
- Delete overlapping programs and duplicate start times.
- Check for stuck manual runs or test cycles.
- Inspect for wiring shorts between zone and common.
If the controller is the cause, the zone stops as soon as you pull its wire or unplug the unit. Clean programming resolves many repeat runs.
Gear And Links You’ll Use
Having the right tools makes each fix faster. Keep a small kit in a tote so you can get to the box and wrap up before the lawn puddles.
| Tool/Part | What It Does | When To Grab It |
|---|---|---|
| Valve Diaphragm Kit | Replaces worn rubber and bonnet seal | Weeping valve or torn/warped diaphragm |
| Replacement Solenoid (24 VAC) | New coil and plunger | Problem follows the solenoid after swap |
| Gel-Filled Wire Connectors | Waterproof splices in the box | Any time you redo zone/common splices |
| Screwdriver & Nut Driver | Open bonnet and bleed ports | Cleaning, flushing, reseating |
| Teflon Tape & Spare O-Rings | Seal threads and refresh gaskets | After service leaks or rebuilds |
| Plastic Basin & Towels | Catch water and mud | Any open-body service |
Model-Backed Guidance You Can Trust
Industry documents and support pages point to the same root causes and fixes you just used: debris inside the body, diaphragm wear, and solenoid faults. For reference, see Hunter’s valve not closing guide and Rain Bird’s Valve Troubleshooting & Maintenance. Both outline cleaning the diaphragm and seat, using the flow control during service, and replacing worn parts when needed.
Backflow And Safety Notes
The backflow device keeps irrigation water from entering the potable line. It sits above grade and must stay intact and sealed. When you shut those two ball valves at the device, you isolate the yard piping only. Follow local code and keep the device protected from freeze and damage.
When A Pro Makes Sense
Call an irrigation tech when any of these show up:
- Repeated zone run-ons after a full clean and diaphragm swap.
- Electrical shorts you can’t trace or a controller that trips breakers.
- Backflow leaks, broken bonnets, or cracked bodies.
Bring notes: which zone runs, what tests you tried, and any part numbers. That cuts labor time and speeds the repair.
Keep It From Happening Again
Simple Preventive Moves
- After line repairs, run a manual flush on each zone before normal watering.
- Open and close the bleed briefly once per season to clear grit.
- Keep valve boxes clear of soil wash-ins and roots.
- Label each zone wire in the controller and in the box.
Seasonal Care
In freeze-prone areas, winterize on time. Shut irrigation supply and drain or blow out lines so trapped water doesn’t split parts or tear diaphragms.
Quick Decision Tree
Zone Still Running Right Now?
Shut water at the backflow → Unplug controller → If water still runs, service the valve (clean or rebuild). If water stops only with power off, fix programming or replace faulty controller parts.
Cleaned The Valve And It Still Weeps?
Install a new diaphragm kit. If seepage continues, replace the valve body.
One Zone Runs With Others?
Check for crossed wires and remove duplicate start times.
Wrap-Up: Fast Shutoff, Smart Tests, Lasting Fix
Stop the water first at the backflow. Separate control from plumbing with the unplug-test. Clear debris, reseat or replace the diaphragm, and swap the solenoid if needed. Update programming and wiring where the tests point. The steps here match brand guides and solve the bulk of stuck-on cases with simple tools and a steady plan. For deeper brand specifics, lean on the linked factory pages in the section above—concise, direct, and field-proven.