Irritrol RD-600: Pump Relay Trips on Zone 3 - Shorted Solenoid

Florida lake-pump system. Any zone starts pump for 1-2 seconds, then relay trips. LED shows "3". Tapping sound from valve box until switch turned off. Filter clogged with algae.

Diagnosis: Zone 3 Solenoid Short

The controller displays "3" indicating zone 3 has a short circuit. When controller energizes zone 3, the short trips the pump start relay (which shares the controller's power supply).

Fix

1. Open controller, note wire color on terminal 3
2. Go to valve boxes, find valve with that same wire color
3. Replace that valve's solenoid (~$8 at Home Depot)

Why Pump Relay Trips

The short on zone 3 pulls excessive current through the controller's internal power supply, causing voltage sag that drops out the pump start relay coil.

Algae Filter Note

Clean the filter, but it's unrelated to the electrical short. The short is in the zone 3 solenoid or its wiring.