Zone 3 Only Runs with Bleed Open: Troubleshoot Voltage & Diaphragm

If zone 3 only runs when bleed screw is open, and swapping valves didn't help — the issue is electrical or diaphragm-related.

Electrical Test (Need Voltmeter)

1. At controller: run zone 3, measure zone 3 terminal to common → 24 VAC?
2. At valve splice: same measurement → voltage drop = wire fault.
3. Solenoid bench test: disconnect, apply 24 VAC directly → clicks?

Diaphragm Check

If voltage good at valve but won't run closed — diaphragm may not lift fully due to debris or weak solenoid plunger.