Rain Dial RD-600 Timer Flashes and Pump Surges Briefly Then Stops

Controller or Pump Start Relay Fault

An outdoor Rain Dial RD-600 timer flashes when a start time is reached. The above-ground water line surges for a few seconds, then stops, and the timer flashes again. Occasionally it runs a full cycle, but mostly it fails.

Diagnostic Procedure

1. Set the controller to zone 1. Measure voltage between COM and zone 1 terminals. Should be 23–27 VAC.
2. If voltage is low, disconnect the zone 1 wire and retest. If voltage returns, the field wiring has a short.
3. If voltage is still low, disconnect the MV/PUMP wire and test COM to zone 1 again. If voltage returns, the pump start relay is drawing too much current (or its coil is faulty).
4. If voltage remains low with all field wires disconnected, the controller itself is defective.

Likely Culprit

Given the intermittent behavior and the brief water surge, the pump start relay is the most probable cause. Its coil may be drawing excessive current intermittently, tripping the controller's overcurrent protection and causing the flash. Replace the pump start relay.