Spring Startup: Backflow Preventer Poppet Won't Seat

Symptom: Water Flows Out Top of Backflow Preventer

After winterization, turning on main water causes flow from the backflow preventer's vent (under the bonnet). The poppet isn't seating.

Fix Steps

1. Turn main valve on more quickly—surge helps poppet seat.
2. If still leaks: poppet or bonnet cracked from freezing—replace the backflow preventer.
3. Check for manual drain valves on mainline (often left open for winter). Close them.

Identify Drain Valves

Look for small valves (petcocks or ball valves) on the mainline between the backflow and zone valves. Close all.