Troubleshooting a Single Zone Failure in a Five-Zone Sprinkler System

When a single zone in a multi-zone irrigation system fails to operate while the others work perfectly, the issue is often isolated to that zone's valve or supply line. In this case, a Toro system with five zones had zone two delivering water—audible flow at the valve and bubbling at the heads—but insufficient pressure to pop up the sprinklers.

Diagnosing the Problem

The user confirmed the solenoid functions and the valve itself passes water, yet the four heads on zone two only bubble. This suggests the valve is opening but not fully, or a restriction exists downstream. Since the system was winterized and no physical damage is evident, the most common culprit is the valve's flow control setting.

Recommended Fix

First, locate the flow control knob on the zone two valve (usually the largest knob on top). Ensure it is opened at least halfway. If that doesn't restore full pressure, the valve may need disassembly and servicing—debris, a torn diaphragm, or worn internal parts can prevent full opening. A detailed tutorial on valve repair is available at Irrigation Tutorials.

If the flow control is already open and the problem persists, inspect the valve interior for obstructions or diaphragm damage. Replacing the diaphragm and cleaning the valve body often resolves the issue without requiring a full valve replacement.