Backflow Preventer Petcock Leaking at Spring Startup

Water shooting from an unplugged petcock (test cock) on the backflow preventer after winterization means the test cock wasn't closed—they're left open for winter drain.

Fix

1. Locate the slotted screw on the leaking petcock.
2. Insert screwdriver, turn ¼–½ turn clockwise to close.
3. If it won't seal (common on old brass), install a 1/8" NPT brass plug (~$2) or replace petcock.

Why One Has a Plug

The plugged petcock likely had a damaged seat. Previous installer plugged it instead of replacing. Do the same for the leaking one if it won't close.

Petcock Purpose

Only for winter drainage. No role in backflow prevention. Closing or plugging them is correct for operation.

Full Startup Checklist

• Close both ball valves slowly (10 sec each) to avoid water hammer.
• Close all 4 test cocks (slots vertical = closed).
• Pressurize, check for leaks.
• Run each zone, verify coverage.

Simple fix—don't call a pro for this.