Most Likely Causes (Ranked)
Sprinkler heads sit at ground level and take constant abuse — lawnmowers, foot traffic, freezing, and UV degradation all crack the plastic body. A cracked head leaks during operation, sending water in wrong directions and reducing pressure to other heads on the zone. Pop-up heads are most vulnerable because they protrude during mowing.
PVC or poly lateral lines crack from freeze damage, root pressure, settling, or shovel/edger strikes during landscaping. Main supply lines are typically 1-inch PVC and handle higher pressure — when they fail, the volume is significant. Fittings (tees, elbows) are the weakest points.
Each zone has an electric solenoid valve in a valve box. The valve diaphragm, solenoid plunger, or jar-top O-ring wears out after 10-15 years. A leaking valve causes water to seep through the zone even when it's supposed to be off, or leaks from the valve body into the valve box.
Threaded fittings (especially at the point where risers connect to lateral lines) crack from lawnmower impact transmitted through the sprinkler head, from overtightening during installation, or from freeze damage. Swing joints (flexible risers) reduce this risk but aren't used in all systems.
The backflow preventer (RPZ or PVB) prevents irrigation water from contaminating your drinking water. These devices have internal check valves and relief valves that wear over time. A leaking backflow preventer drips or flows continuously from the relief port.
How to Fix It
Replace a Sprinkler Head
$3-8 per head- 1Dig around the head to expose the riser. Unscrew the head counterclockwise.
- 2Screw on the new head (same brand/model for matching spray pattern). Use Teflon tape on threads.
- 3Flush the line briefly before installing the new head to clear debris.
- 4Adjust the spray pattern and radius to match the original coverage.
Repair a Broken Pipe
$10-30 DIY- 1Locate the leak by probing for soft, wet soil along the pipe run (or use the isolation method: cap each head one at a time).
- 2Dig to expose the broken section. Cut out the damaged piece with a PVC saw.
- 3Install a repair coupling (slip fix) — these telescope to bridge the gap without digging up more pipe.
- 4Prime and cement PVC connections. Let cure 2 hours before pressurizing.
Rebuild or Replace Zone Valve
$15-40 per valve- 1Turn off the water supply. Open the valve box.
- 2For a diaphragm rebuild: disassemble the valve top, replace the diaphragm and spring ($10-15 rebuild kit).
- 3For full replacement: cut the old valve out, install the new one with PVC couplings.
- 4Most valves are Rain Bird or Hunter — match the brand for drop-in replacement.
When to Call a Professional
A leaking main line wastes water 24/7 (not just when the system runs). Your water bill can spike hundreds of dollars in one month.
Leaks near the foundation can undermine the footing — fix immediately if water is pooling near the house.
Shut off the irrigation supply valve as a temporary measure until you can repair.
Don't use the system in freezing weather — winterize with compressed air before the first freeze.
How to Prevent It
Winterize (blow out) the system before the first freeze every year.
Replace sprinkler heads proactively when they show cracks or poor spray patterns.
Mark sprinkler head locations before mowing to avoid lawnmower damage.
Have the backflow preventer tested annually (required by code in many areas). Cost: $50-100.
Frequently Asked Questions
Walk the yard while each zone runs — look for soggy spots, geysers, or areas with extra-green grass. Check your water meter: if it moves with all zones off and the irrigation supply open, you have a main line leak.
Head replacement: $5-10 DIY. Pipe repair: $10-30 DIY or $75-200 pro. Valve rebuild: $15-40. Full winterization: $50-100 pro.
Repair if: the pipes are PVC (long-lasting), issues are isolated, and the layout still works. Replace if: the system uses poly pipe that's failing throughout, or your landscaping has changed significantly.
Most sprinkler repairs are beginner-to-intermediate DIY. The hardest part is finding the leak and digging. Parts are inexpensive and widely available at hardware stores.