Closed the #1 Shutoff and Left It All Winter?
If you closed the irrigation shutoff and walked away, there’s a short pipe section between that valve and the backflow that can stay full of water. In cold weather, that “stub” and the backflow body are the first things to freeze and crack. Here’s exactly how I assess, vent, drain, and finish the season safely—plus what to do if it’s already frozen.
What “#1 Shutoff Only” Leaves Full
Between the main irrigation shutoff (#1) and the backflow is a short length of pipe. Close #1 and leave—this stub often stays full, chills fast, and can split.
If the test cocks weren’t opened, the backflow shell can hold a slug of water. That’s a crack waiting to happen.
Without a proper blowout, low spots in laterals and tall spray bodies can keep “cups” of water that freeze and break fittings or cans.
Typical Symptoms You’ll Notice
- Slow drip at the drain or backflow days after you “shut it down.”
- Wet seam or hairline crack on the backflow body once temps bounce above freezing.
- In a cold snap, the copper stub feels like a solid ice bar.
- In spring, zones won’t pressurize or you find broken tall spray bodies (12″ cans) near driveways/sidewalks.
If It’s Not Frozen Yet: Do This Now (5–10 minutes)
- Keep the irrigation shutoff closed.
- Open both backflow test cocks (the small slotted ports). This vents the shell so it cannot hold water.
- Crack the drain plug (remove or leave partially threaded) so any seep past the shutoff drips out, not back into the system.
- Plan a proper blowout: zone-by-zone at modest pressure (≈50–60 PSI) with high airflow until each zone finishes on a mist. Don’t try to make up for low airflow with high PSI.
- Check the drain area in 24–72 hours. If it’s still dripping steadily, the shutoff is likely weeping and should be replaced—your open drain prevented refilling the lines (that’s good).
If It’s Already Frozen: Safe Recovery Steps
- Confirm the house main and electrical near the work area are safe/dry.
- Do not crank PSI to “push ice” away—this breaks parts.
- Use steady, controlled electric heat (heat tape or a dryer at a safe distance) to gently warm the stub/backflow area.
- Avoid open flame on plastics, gaskets, wiring, or near siding.
- Open test cocks; loosen the drain plug to give thawed water an exit.
- Once thawed and safe, proceed to a proper blowout so the rest of the system isn’t left holding pockets.
- Look for split shells, bent poppets/bonnets, distorted seats.
- Even if the backflow needs replacement, we can still protect the yard by clearing the laterals/heads now.
Finish the Season the Right Way (My Playbook)
- Connect downstream of the backflow to protect it during the blowout.
- Run each zone from farthest to nearest. Aim for mist, not “bone dry” blasting.
- Use short, cool passes once mostly air is coming through to avoid heat on dry parts.
- Leave test cocks open and the drain plug off/partially threaded for 24–72 hours.
- Document anything suspicious on a paper Winterizing Report (I leave this behind) so spring repairs are straightforward.
Notes for Pump/Lake/Well Systems
- Disable pump-start/master valve in the controller.
- Switch the pump breaker OFF at the electrical panel and label it.
- Proceed with the same vent/drain steps and full blowout to mist.
Prevention Checklist for Next Fall
- Open both test cocks so the backflow can’t hold a slug.
- Leave the drain plug off/partially threaded to catch a weeping shutoff.
- Run enough airflow at modest PSI to reach a clean mist on every zone.
- City water: leave controller ON; optional long Rain Delay if you like a “paused” status.
- Pump systems: controller ON, pump-start disabled, breaker OFF.
- Check the drain area in 24–72 hours. Ongoing drip = weeping shutoff (plan replacement).
- Keep the paper Winterizing Report for spring start-up.
FAQ
Yes. Closing #1 doesn’t clear laterals, tall spray bodies, or the backflow shell. A blowout moves water to the nozzles and finishes on mist.
No. High PSI without volume breaks parts and creates fog. Use adequate airflow at modest pressure.
Persistent drip usually means the shutoff is weeping. Your open drain prevented refilling the system—replace the valve when convenient.
Not necessarily. We can still isolate and clear the rest now to avoid a yard full of spring breaks, then replace the backflow when parts are available.