Zone Works Manually But Not Electrically: Valve Opening Issue

Full Flow Manual, Half Flow Electrical: Valve Diagnosis

One of 3 backyard zones operates at full pressure manually but only 50% pressure electrically. Solenoid, controller, and wiring all replaced. Voltage at valve confirmed.

Root Cause: Valve Not Opening Fully Under Solenoid Power

The solenoid provides insufficient force to fully lift the diaphragm against system pressure, but manual bleed (which vents the upper chamber directly) works perfectly.

Targeted Fixes

1. Verify 24VAC at valve under load: Measure at solenoid leads while controller activates zone
2. Clean valve internal ports: Tiny passages in valve body/bonnet can restrict pilot flow
3. Adjust flow control: Full open → full closed (count turns) → half open
4. Replace valve bonnet assembly: If ports clean and voltage good, diaphragm/spring assembly is worn

This is a known failure mode on older valves where the solenoid's magnetic force degrades or the diaphragm loses elasticity.