Single Zone Failure in 5-Zone System: Electrical Troubleshooting

Zone 4 Not Working: Systematic Diagnosis

One of five zones suddenly stopped working. Other four zones operate normally.

Step-by-Step Isolation

1. Check valve wire connections — clean corrosion, replace wire nuts
2. Verify controller terminal output — 24VAC at zone 4 terminal during run time
3. Cross-test: Connect zone 4 wire to working zone terminal — if valve operates, controller terminal is bad
4. Cross-test: Connect working zone wire to zone 4 terminal — if valve operates, wiring/valve is good, controller issue
5. Test solenoid directly — disconnect at valve, apply 24VAC from known-good source

Most Likely Culprits

• Corroded wire connectors at valve (very common)
• Failed solenoid (coil open or plunger stuck)
• Controller terminal failure (relay or triac)

Start at the valve—it's the highest-probability, easiest-to-fix location.