A patch of lawn that stays wet when everything's dry, or a zone that suddenly waters at half strength — both usually mean a broken pipe somewhere underground. The trick to finding it isn't a metal detector; it's paying attention to one thing: timing.
How do you tell a mainline leak from a zone leak?
The key tell is timing. A mainline leak stays wet even with the system off — it's under constant pressure. A zone leak only appears when that zone runs. Locate it by the soft, sunken or greener patch directly above the break.
Your system has two kinds of pipe. The mainline is live whenever the water supply is open — it carries pressure to the valves around the clock. The lateral (zone) pipes only see pressure when their valve opens for that zone's run. That difference is your whole diagnosis:
- Wet with the system completely off → mainline. It's leaking 24/7, so the spot never dries.
- Wet only when one zone runs → a lateral on that zone. Dry the rest of the time.
How do you actually find the break?
Once you know which kind it is, finding it is mostly observation:
- For a zone leak, run the suspect zone and walk it. Look for water bubbling up through the turf, a weak geyser, or a patch that goes soft and squelchy fast.
- Watch for a patch that greens up or grows faster than the lawn around it — a slow underground leak fertilises and waters that spot for weeks.
- For a mainline leak, look for the always-wet spot with everything off. Follow the line from the supply toward the valves; the lowest, softest, never-drying ground is usually right over the break.
- Note pressure clues. One zone suddenly weak, or every zone weak, narrows down whether it's a lateral or something closer to the main.
Why do sprinkler pipes break?
In the GTA, a handful of causes account for most breaks:
- Winter freeze on a poorly drained line — water left in a low spot expands and splits the pipe or a fitting. The number-one reason a good winterization matters.
- Ground settling and frost heave — soil moves over the years and stresses rigid joints.
- Tree roots — growing roots wrap and crush irrigation pipe over time.
- Aeration, digging or fence posts — a lawn-aerator tine or a shovel through a shallow line is a classic mid-season break.
- A stuck valve spiking pressure — a valve that hammers shut can spike pressure and pop a weak fitting downstream.
Can I fix it myself?
Honest answer: a clean break in a lateral (zone) pipe is DIY-able for a confident homeowner — expose it, cut out the damaged section, and join in a new piece with a slip coupling. Cap the water, take your time, and keep the trench clean.
What's not worth the gamble: mainline and valve-box leaks are under constant pressure, the fittings are less forgiving, and wrong-spot digging is how a single-fitting repair turns into a landscaping rebuild. If you're unsure which pipe you've got, or the water won't stop, that's the line to hand off. (If the leak is actually at a head with the system off, it may be a valve instead — see water pooling around a sprinkler head.)
How does PJL repair a broken pipe?
A standard break is a flat-price repair — clamps and fittings included — so you know the number before we dig. A mainline repair is custom-quoted, because depth, length and what's on top of it (a patio, a mature bed) all change the job. Either way you see the price first; the structure is on our pricing page, and the work carries our repair warranty.
Run it through our AI diagnostic tool first — if its diagnosis matches what we find on site, you get one hour of repair labour free. More on what we cover on the sprinkler repair page.
Frequently asked questions
How do I know if my sprinkler leak is the mainline?
Turn the whole system off and watch the wet spot. If it stays wet — or keeps refilling — with everything off, it's the mainline, because that pipe holds pressure all the time. If it only appears when a zone runs, it's a lateral on that zone.
Why is one patch of my lawn always wet?
A constant wet patch is almost always an underground leak feeding it — usually a mainline crack or a passing valve. That spot often grows greener and faster than the rest of the lawn because it's being watered and fertilised around the clock.
What causes a sprinkler pipe to break?
In the GTA the usual suspects are winter freeze on a line that didn't drain, ground settling and frost heave, tree roots, and physical strikes from aerating or digging. A stuck valve spiking pressure can also pop a weak fitting.
Will a leak raise my water bill?
Yes — and a mainline leak especially, because it runs 24/7. Even a slow underground leak can add up quickly over a billing period, which is why a spot that never dries is worth chasing down.