Why Wet Spots Between Cycles Happen

A properly functioning irrigation system should leave the ground dry between scheduled watering windows. Wet spots that persist or reappear hours after a zone finishes point to one of three causes: a valve that isn't sealing fully (valve bleed), a leak in the lateral pipe, or a scheduling conflict that runs overlapping zones.

Common Symptoms

Soil stays visibly damp in one area after the rest of the zone has dried
Wet patch appears hours after the irrigation cycle ends
Water pooling or running on the surface near a single head
Soggy area persists for days after the system ran
Puddle forms in a location with no head nearby (underground lateral leak)

Diagnostic Steps

Confirm it is irrigation-related. Note whether the wet spot corresponds to a specific zone and whether it gets worse after that zone runs. If the same spot stays damp after dry weather with no irrigation, a utility leak or groundwater issue may be the cause — not the irrigation system.
Run the zone and watch the valve. Activate the suspected zone. Stand at the valve and listen: a healthy valve is silent when closed. A valve that is bleeding will produce a faint hissing sound even when the zone is supposedly off. Place your hand near the solenoid — some bleed leaks are audible only under the bonnet.
Check for valve bleed using the bleed screw. Turn the manual bleed screw on the valve 1/4-turn counter-clockwise. If water flows continuously without the zone being active, the valve diaphragm or pilot circuit is failing to hold — the valve is permanently partially open.
Walk the pipe run during a zone cycle. With the zone running, watch the ground between heads. A lateral pipe leak produces visible bubbling or heaving soil, or a concentrated wet patch that grows during the cycle. Walk back after the zone shuts off — a lateral leak will continue to seep after the water is off, keeping the spot wet for hours.
Check for scheduling overlap. Review the controller program for overlapping run times. Two zones that share a common supply pipe can create the illusion of a leak if they run simultaneously, sending water to the same lateral line at double the intended flow and causing overspray or seepage at the lowest head on the shared run.
Inspect the zone valve diaphragm. Remove the valve bonnet and examine the diaphragm. A torn, hardened, or misshapen diaphragm cannot form a positive seal against the valve seat, allowing water to percolate through even when the solenoid is de-energized. This is the most common root cause of a slow bleed.
Verify the solenoid seats properly. Remove the solenoid and check that the small rubber gasket on its base is intact and not swollen or cracked. A damaged solenoid base gasket can cause a slow leak past the solenoid port.

Root-Cause Summary

Valve diaphragm failure — most common; the valve cannot seal and bleeds water continuously
Failed solenoid base gasket — allows water to bypass the diaphragm seal at the solenoid mount
Lateral pipe leak — cracked fitting, glued joint failure, or frost-heave crack; seepage continues between cycles
Scheduling overlap — two zones share a lateral line and run simultaneously, over-pressuring the shared pipe
Zone valve not fully closing — debris under diaphragm or damaged valve seat prevents complete shut-off

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