Fixing a Zone That Won't Shut Off: Nelson 8424 System

Your Nelson 8424 system's Zone 3 leaks water when the system should be off, and shutting it off at the controller doesn't work. Even after rebooting and reprogramming, the zone activates as soon as water is restored. This points to a mechanical valve failure, not a controller issue.

Root Cause: Solenoid or Diaphragm

The valve isn't closing fully because either:

• The solenoid is stuck open (failing to release the plunger), or
• The diaphragm is torn, debris-blocked, or installed incorrectly.

Since you don't know the exact valve model, replace both components—it's faster and ensures a complete fix.

Step-by-Step Replacement

1. Shut off water to the irrigation system.
2. Remove the solenoid: Unscrew it from the valve body. Note wire connections, then attach wires to the new solenoid identically.
3. Replace the diaphragm: Remove the valve bonnet screws, lift off the bonnet, swap the old diaphragm for a new one, and reassemble. Ensure the diaphragm seats properly and the spring (if present) is in place.

Helpful Resource

For visual guidance, visit irrigationtutorials.com—they have detailed valve rebuild tutorials.

Once both parts are replaced, Zone 3 should operate normally. Good luck!