Sprinkler Coverage Gap - Diagnostic

Symptom

Customer reports brown patches in the lawn even though the sprinklers are running. The diagnostic distinguishes coverage problems (not enough water reaching the spot) from pressure problems (water reaching but too lightly) from controller problems (system isn't running at all in the schedule the customer thinks).

Likely Causes

In order of frequency:

• Heads not popping up fully (low pressure OR plugged riser) - 25 % of coverage complaints
• Head spacing too wide ("dry corners") - 18 %
• Misaligned head direction - 15 %
• Failed head (cracked nozzle, broken gear) - 10 %
• Pressure too low at the head - 10 %
• Controller program error (zone disabled or timing off) - 8 %
• Failed valve (zone not running when controller calls) - 8 %
• Clogged nozzle - 6 %

Diagnostic Steps

1. Run the system manually. Stand at the affected area while the zone runs. Visual check:

• Is water reaching this spot at all?
• Are heads popping up fully (4" residential pop-up height standard)?
• Is spray pattern even, or weak/sputtering?

1. Map the dry spots vs head locations. Sketch on paper. Common patterns:

• Spot in middle of overlap = head spacing too wide OR pattern wrong
• Spot at corner of property = no head reaching that corner; add a head
• Spot near a head = head not rotating or pop-up issue at that specific head

1. Inspect the head at the problem location:

• Pop-up height correct?
• Nozzle clear (no dirt or debris)?
• Pattern set correctly (matches the intended spray area)?
• Rotor head: does it rotate the full programmed arc?

1. Test pressure at the zone. Most residential systems need 30 - 50 psi at the head:

• Below 30 psi: insufficient pressure; heads don't pop up fully or spray weakly
• Above 80 psi: misting + drift; water never reaches the intended area

1. Check the controller. Run each zone manually for 2 minutes; verify each starts on cue.

Resolution

• Head won't pop up: clean the riser; replace the head if internal seal is failing.
• Head spacing too wide: add a head OR widen the existing pattern; quote the customer for the install.
• Misaligned direction: rotate / re-set the pattern per the head's manual.
• Failed head: replace; match brand + nozzle type to maintain consistent coverage.
• Pressure low: check the main supply pressure; could be the main shutoff partially closed OR a leaking line upstream.
• Pressure high: install a pressure regulator at the head OR upgrade to pressure-regulating heads.
• Controller error: customer education on the program; verify the zone is enabled + the run time is sufficient.
• Valve failure: replace solenoid first (cheap, common); valve body if solenoid doesn't fix.
• Clogged nozzle: clean with a small wire or replace.

Prevention

• Spring start-up walkthrough catches misaligned heads + low pressure before browning shows
• Annual head replacement on any showing wear (worn nozzles spray inefficiently)
• Customer education on running the system during early morning (less evaporation, less wind drift)

References

• Irrigation Association best practices
• Manufacturer literature (Rain Bird, Hunter, Toro)
• Manuall internal: Spring Lawn Startup Service, Yellowing Grass - Diagnostic Tree