Diagnosing Irrigation System Faults
Separate electrical faults from water faults, test controllers, wires and solenoids with a meter, read pressure and flow, and handle backflow and coverage problems.
Table of contents
A customer tells you the sprinklers are broken. That could mean a dead transformer, a nicked wire under a driveway, a torn diaphragm, a dirty nozzle, a leak at a fitting, or a program someone changed. Replacing parts until something works is slow and expensive. A good tech asks one question first: is this an electrical fault or a water fault? One simple test answers it, and everything after that is a shorter search.
What You Will Be Able to Do
- Split any zone fault into electrical or hydraulic with one test
- Use a multimeter to test a controller, field wiring, and solenoids
- Read static and working pressure to find a hydraulic fault
- Use the water meter to measure a zone's flow and find leaks
- Tell low-head drainage from a leaking valve
- Measure coverage with a catch-can test
Start With the Split Test
Before you dig, find out which side of the valve has the problem. Go to the valve for the zone that is not working.
- Open the valve by hand. Most valves have a bleed screw, or a solenoid you can turn about a quarter turn counterclockwise.
- Watch the heads.
| Result | What it means | Next step |
|---|---|---|
| Valve opens by hand, heads run | Water side is fine | Test the electrical side |
| Valve will not open by hand | Water side has the fault | Check supply, flow control, and diaphragm |
| Opens, but heads are weak | Hydraulic fault downstream | Check pressure and flow |
Close the bleed screw or solenoid afterward, and go easy on it. An overtightened solenoid is hard to remove, and a loose one leaks.
Electrical Faults
Field wiring runs about 24 volts AC, which you can test with a multimeter. Keep your work on the low-voltage side of the controller. The line-voltage side is for a qualified electrician.
Warning: Set your meter to AC volts for voltage tests and turn the power off for resistance tests. A wet valve box around a working solenoid is a low-voltage risk, but a controller's power supply and any pump circuit carry line voltage. If a pump start relay or line-voltage wiring is involved, stop and call a qualified person.
Which Zones Are Affected?
- All zones dead. Check for no display, a blown fuse or tripped breaker in the controller, a bad transformer, or a broken common wire.
- Several zones dead. Suspect a shared wire or a shared splice.
- One zone dead. Suspect that zone's solenoid, wire, or terminal.
Testing at the Controller
- Check the transformer. With the controller powered, measure AC volts at the 24 VAC terminals. One major maker expects about 24 to 28 volts. A much lower reading means a bad transformer or too heavy a load.
- Check the station output. Run the zone. Put one probe on the common terminal and the other on the zone's terminal. You should see about the same voltage. No voltage means the controller is not sending it, so look for a program fault or a blown station.
- Test the circuit. Turn off the zone and disconnect its wire from the terminal. Measure ohms between the zone wire and the common wire. The reading tells you about the wire and solenoid together.
| Reading | Likely meaning |
|---|---|
| 0 to 5 ohms | Short, either a shorted solenoid or wires touching |
| 8 to 20 ohms | Shorted solenoid, or more than one valve on the zone |
| 20 to 60 ohms | Normal for a single solenoid |
| Above 60 ohms | Bad splice, nicked wire, open solenoid, or a broken wire |
These values come from one major maker's guide. Other makers differ a little, so compare with a known good zone on the same site. A good zone of the same type is your best reference.
Isolating the Solenoid
Go to the valve and disconnect the solenoid from the field wires. Test it alone.
Worked example. Zone 7 will not run. At the controller, you read over 1,000 ohms, which points to an open circuit. At the valve, you disconnect the solenoid and measure 38 ohms across it, which is fine. The solenoid is good, so the break is in the wire. You check the splice in the box, and it is green with corrosion. You cut it back to bright copper and make a new splice with a waterproof connector. The reading at the controller now comes back at 41 ohms, and the zone runs.
Finding Wire Faults
A nick in the insulation lets water reach the copper. Over time, the wire corrodes through.
- Look in valve boxes first, because most faults happen at splices.
- Think about recent digging, new fences, aeration, and driveway work.
- Use a spare wire if the bundle has one, and label it. Move the zone to the spare until you can repair the break.
- A wire tracker sends a signal along the wire, so you can follow it and find the break. A locator can also find a lost valve box.
Use only splice connectors rated for direct burial. A wire nut with tape will fail. Never leave a splice in the soil where nobody can reach it. Put it in a box.
Hydraulic Faults
A pressure gauge and the water meter show what the water is doing.
Static and Working Pressure
Read pressure at the same point with nothing running, then with the zone running. The drop tells you how hard the system is working.
Worked example. Static pressure is 65 psi. The design said about 50 psi at the valve with Zone 3 running. You measure 31 psi. Something is taking more flow than designed, or the supply is partly choked. If the meter shows flow well above the design, look for a break or missing nozzles. If the meter shows flow near or below the design, look for a partly closed valve, a clogged filter, or a failing pressure regulator.
Reading the Meter
Read the water meter over a timed run and work out the flow.
Worked example. Zone 4 is designed for 12 GPM. You run only that zone for 5 minutes, and the meter moves 75 gallons. 75 divided by 5 is 15 GPM. That is 3 GPM over the design. Look for a break, a missing nozzle, a wrong nozzle, or a head with a broken seal. Walk the zone at the lowest point first.
Finding a Leak
With all zones off and nothing running in the building, watch the small leak indicator on the meter. If it moves, water is going somewhere.
- Close the isolation valve for the irrigation system.
- If the indicator stops, the leak is in the irrigation system. It is either a mainline break or a zone valve leaking through.
- If it keeps moving, the leak is on the building side.
Mainlines stay under pressure all the time, so a small break can run for weeks. Look for a wet spot, a greener patch, or soft ground.
When a Zone Will Not Shut Off
A zone that keeps running after the controller stops has a short list of causes. Do this test first: disconnect the zone wire at the controller.
- Valve closes: The controller is holding it open. Check for a program running, a stuck output, or a manual start.
- Valve stays open: The fault is at the valve. Check the bleed screw, the solenoid, and the flow control. Then shut off the water and look for debris in the diaphragm or a tear.
A partly closed flow control or grit under the diaphragm can both stop a valve from sealing. Follow the rebuild steps for that model, then test.
Weeping Heads
Water from the lowest heads after a zone shuts off does not always mean a bad valve.
| What you see | What it is | Fix |
|---|---|---|
| Stops after minutes, once the lateral is empty | Low-head drainage | Check valves in the heads |
| Runs for hours, never stops | Valve leaking through | Clean or rebuild the valve |
Worked example. A low head dribbles after each run, then stops after about 10 minutes. The lateral above it holds water, and gravity empties it through the lowest head. The valve is fine. A check valve at the head fixes this.
Water Hammer
Banging at valve shutoff means the water stopped too fast. High pressure and fast water make it worse. Check that speed in the pipe is under 5 feet per second and that the static pressure is sensible. Slow-closing valves and arrestors help. Spring start-up can cause the same thing, so fill lines slowly, with a zone open to let the air escape. Air trapped in a line can slam a valve and crack fittings.
Head and Coverage Problems
| What you see | Likely cause | Fix |
|---|---|---|
| Misting and drift | Pressure too high | Add pressure regulation |
| Short throw, doughnut pattern | Pressure too low, or a clogged screen | Check pressure and clean the filter |
| One head stuck down | Grit, or a worn seal | Flush or replace the head |
| Dry spot between heads | Gaps in coverage, wrong arc, or a tilted head | Adjust and check head-to-head spacing |
| Rotor not turning | Debris or a stripped drive | Clean or replace |
| Ponding on the low side | Run too long, or low-head drainage | Add cycle and soak, or check valves |
Catch-Can Test
A catch-can test turns a complaint about dry spots into a number. Set out identical straight-sided cans in a grid across the zone. Run the zone for a set time, then measure the water in each can.
Distribution uniformity (DU) is the average of the lowest quarter of cans divided by the average of all cans.
Worked example. You set out 12 cans. Their average is 0.46 inches. The 3 lowest read 0.27, 0.30, and 0.33, so their average is 0.30. DU is 0.30 divided by 0.46, or about 0.65. Next, you look at where those low cans were. If they all sit along one line of heads, you may have a pressure or spacing problem. If they sit around one head, check that head.
Backflow Faults
Backflow assemblies protect drinking water, so you must treat them carefully. Testing is done by a certified tester. In many areas, repairs on a testable assembly must be followed by a retest. Follow local rules on who may do the repair.
| Symptom | What it may mean | What to do |
|---|---|---|
| PVB spits briefly at start-up | Normal as it seats | Watch it |
| PVB leaks steadily from the vent | Worn or fouled seat | Rebuild and retest |
| Cracked body after winter | Freeze damage | Replace and retest |
| RPZ dumping water from the relief port | Fouled check or relief valve | Report it, and do not plug the port |
| No water to the system in spring | Closed shutoff or test cock left open | Check isolation valves |
Warning: Never cap, plug, or bypass a backflow device to stop a leak or to get a zone running. If the device fails, shut off the system and call for a repair and retest. A bypass connects the lawn to the drinking water.
Work the Same Order Every Time
- Ask what changed: recent digging, a power outage, or a new program.
- Check the controller: time, program, sensor bypass, and rain delay.
- Do the split test at the valve.
- For electrical faults, use the voltage, then ohms.
- For water faults, read pressure and meter flow.
- Fix the cause, and run the zone to prove it.
- Record what you found on the controller chart and work order.
Common Mistakes
| Mistake | What it costs |
|---|---|
| Replacing a solenoid before testing it | A wasted part, and the broken wire stays |
| Digging before doing the split test | Hours spent on the wrong side |
| Rebuilding a valve for low-head drainage | Wasted time, and it keeps dripping |
| Burying a splice | A fault nobody can find later |
| Plugging an RPZ relief port | A hidden failure and a contamination risk |
| Leaving a tested zone in manual | A zone that runs all night |
Check Your Understanding
1. You turn a zone's solenoid by hand, and the heads run fine. The controller shows the zone is on, but nothing happens. Which side has the fault?
The electrical side. The water side works, so test voltage at the terminal, then ohms on the wire and solenoid.
2. You read 3 ohms on a zone from the controller. What does that tell you, and what do you do next?
A short. Disconnect the solenoid at the valve and test it alone. If it still reads low, replace it. If it reads normal, the wires are touching somewhere, so check the splices.
3. A zone designed for 10 GPM moves 70 gallons on the meter in 5 minutes. What do you think?
70 divided by 5 is 14 GPM, or 4 GPM over the design. Look for a break, a missing nozzle, or the wrong nozzles.
4. With everything off, the meter's leak indicator is turning. You close the irrigation isolation valve, and it stops. Where is the leak?
In the irrigation system, on the pressurized side. Check the mainline and any valve leaking through.
5. Water is still running from a low head two hours after the zone shut off. What is the likely fault?
The valve is leaking through. Low-head drainage would stop once the lateral emptied. Clean or rebuild the valve.
Key Takeaways
- Do the split test first, by opening the valve by hand.
- A normal solenoid usually reads about 20 to 60 ohms.
- Test wire and solenoid together, then apart.
- Read static pressure, working pressure, and meter flow.
- Low-head drainage stops, and a leaking valve keeps going.
- Never plug or bypass a backflow device.