Pump Start Relay Buzzes Only on Zone 3: Wiring Cross-Talk

Symptom: Relay Chatters on One Zone Only

An 8-zone system with a 3 HP pond pump: pump start relay buzzes loudly only when zone 3 runs. Valve tested OK with 9V batteries.

Likely Cause: Crossed Wires

The zone 3 hot wire is likely shorted to the pump start (MV) wire somewhere between the controller and the valves, causing the relay to chatter when zone 3 activates.

Diagnostic Steps

1. Disconnect all field wires at the controller.
2. Check continuity between zone 3 wire and MV wire (should be open).
3. Inspect wire bundle for nicks, especially at valve box entries.
4. Tighten all controller terminal screws.

If Wiring Checks Out

The controller's output for zone 3 may be leaking voltage to the MV terminal. Try moving zone 3 to a spare terminal (if available) or replace the controller.