A brown patch the sprinklers never seem to reach, or a head soaking the driveway instead of the lawn — coverage complaints are the most fixable problems on a sprinkler system. Most are a five-minute adjustment. The one exception is worth understanding before you start adding heads.
Why does my lawn have dry spots?
Most coverage problems are an adjustment, not a fault: set the spray arc and radius, or the rotor's left/right stops. But you can't always just add a head — every zone has a pressure and flow budget, and past it the real fix is a new zone.
Dry spots come from a short list of causes: heads knocked out of alignment, mismatched heads on one zone, not enough pressure, or heads simply spaced too far apart for the water to overlap. The first three are adjustments. The last one is where people get into trouble adding hardware — more on that below.
How do I adjust a spray head?
Fixed spray heads (the ones that throw a fan, not a rotating stream) have two adjustments:
- Arc — how wide a wedge it covers. On most nozzles you set the pattern by rotating the nozzle collar to the arc you want (a quarter, half, or full circle), centred on the area to cover.
- Radius — how far it throws. The small screw on top of the nozzle is the radius-reduction screw; turning it in cuts the throw back, turning it out extends it. Use it to pull spray off a fence or to stretch to a dry edge.
How do I adjust a rotor?
Rotors (the heads that shoot a single rotating stream back and forth) are set by their travel and reach:
- Set the left stop. The left edge is the fixed start of the arc — rotate the head body so the stream starts where you want the sweep to begin.
- Set the right stop. Use the adjustment (a key or a screwdriver in the top, depending on model) to dial the arc wider or narrower until the stream stops where you want it.
- Set the radius. The radius-reduction screw shortens or lengthens the throw — back it off to reach further, screw it in to keep water off the pavement.
Can I just add another head to a zone?
Here's the honest answer, because it's where most DIY coverage fixes go wrong: only if the zone has spare capacity. Every zone has a flow and pressure budget — a fixed number of gallons per minute it can supply. Add a head within that budget and everything's fine. Add one past it and you don't get more coverage; you get every head on the zone running weak, so you've traded one dry spot for a whole soft zone.
When a zone is already maxed out, the real fix is a new zone — its own valve and supply, sized properly. A new zone starts at $575 and is custom-quoted to the area; see our sprinkler installation page. If the dry spot is really a pressure problem from a leak, that's a different chase — see how to find a broken sprinkler pipe.
How do I stop overspray onto the driveway?
Watering the sidewalk isn't just wasteful — under GTA watering bylaws, runoff onto hard surfaces is exactly what they're written to discourage. Three ways to fix it:
- Adjust the arc and radius so the pattern stops at the lawn edge (the quickest fix).
- Swap the nozzle for one with the right arc or a shorter throw, or an edge/side-strip nozzle for a border.
- Relocate the head if it was set too close to the edge to ever aim cleanly.
When should you call us?
If adjusting doesn't close the gap, if you suspect the zone's out of capacity, or you'd rather have it dialled in properly, we're same-day across the York Region core in season. Coverage tuning is part of what we do on the sprinkler repair page.
Start with the AI diagnostic tool — if its diagnosis matches the on-site fix, you get one hour of repair labour free.
Frequently asked questions
Why does my sprinkler leave dry spots?
Usually heads out of alignment, mismatched heads on one zone, too little pressure, or heads spaced too far apart to overlap. The first three are quick adjustments; spacing that's genuinely too wide may need a head added — but only if the zone has spare capacity.
How do I stop my sprinkler spraying the driveway?
Adjust the arc and radius so the pattern stops at the lawn edge, swap to a nozzle with the right arc or a shorter throw, or relocate a head that sits too close to the edge. It also keeps you onside with GTA watering bylaws on runoff.
Can I add a sprinkler head to an existing zone?
Only if the zone has spare flow and pressure. Every zone has a budget; add a head within it and you're fine, but add one past it and every head on the zone runs weak. Past that point, a new zone is the real fix.
How many heads can one zone run?
It depends on your water pressure and flow and the type of heads — there's no single number. The test is simple: if adding a head makes the others noticeably weaker, you've hit the zone's limit and need a new zone instead.