Irritrol RD-600 Only Outputs 15VAC: Controller or Wiring Fault?

RD-600 works fine but only outputs 15VAC to stations. Transformer reads 24VAC. Multiple transformers tested with same result. Factory reset and new 9V battery didn't help. Needs to run 3 valves simultaneously (old Hardie 6100 did this).

Critical Diagnostic Question

Where are you measuring 15VAC?

• At controller terminals (field wires disconnected) → Controller is defective - internal voltage regulation or output driver failure
• At valve solenoids (wires connected) → Wiring issue (high resistance) or solenoid loading down the output

Testing Procedure

1. Disconnect ALL field wires from controller
2. Activate one zone
3. Measure VAC between that zone terminal and Common
4. Should read 22-26 VAC

If 15VAC at Controller With No Load

The controller's output stage is damaged. Repair or replace. The Hardie 6100 handled multiple valves because it had robust output drivers - the RD-600 may not support 3 simultaneous valves even when healthy.

Simultaneous Valve Operation

Most residential controllers run ONE zone at a time sequentially. Running 3 simultaneously requires either a commercial controller or a master valve/pump start setup where one signal opens multiple valves via a manifold.