Fixing a Sprinkler Valve That Won't Shut Off: Diaphragm Replacement

A homeowner manually activated a zone via the valve's bleed screw for head adjustment, but afterward the valve refused to close—even with the controller off. Water continued flowing until the main supply was shut off.

Understanding the Bleed Screw

The small black knob is a bleed screw. Loosening it releases water from above the diaphragm, allowing inlet pressure to lift the diaphragm and open the valve. This is normal manual operation.

Why the Valve Stays Open

If the valve won't close after tightening the bleed screw, the diaphragm is likely damaged or debris is preventing seating. The diaphragm's rubber seal fails to reseat against the valve body, allowing continuous flow.

Diaphragm Replacement Procedure

1. Shut off main water supply
2. Remove screws from valve bonnet (top)
3. Carefully lift off bonnet—note spring position (don't lose it!)
4. Remove old diaphragm
5. Take diaphragm to irrigation supply store for exact match
6. Install new diaphragm, replace spring, reinstall bonnet
7. Tighten screws evenly in star pattern
8. Restore water and test

This 15-minute repair costs $10-20 for the diaphragm versus $100+ for a service call.