Frozen Backflow? (Real Driveway Stories & What We Do Next)
Hoodie weather, leaves skittering across the driveway, windows cracked just enough to smell October—and then the neighbor texts: “Hey, water’s spraying off the side of your house!” I see this every year across Metro Detroit. Sometimes it’s a backflow shell split open and misting the siding. Other times the copper stub is a popsicle and the valve box is a slushie.
What actually happened (plain English)
- The “stub” stayed full: If #1 shutoff was closed and the backflow wasn’t vented, the short run between shutoff and backflow can sit full. First hard freeze and—crack.
- The backflow body split: The shell held a slug of water; freezing added ~9% volume; plastic/metal lost that argument.
- A weeping shutoff kept feeding it: Even a tiny seep keeps refilling the stub unless there’s a place to drain.
Good news: even if the backflow is toast, there’s often still time to protect the rest of the system before deeper cold sets in.
While you wait for me (homeowner quick steps)
- Kill irrigation water: Close the irrigation shutoff. If spray won’t stop, close the house main temporarily.
- Vent the body: Open the two test cocks on the backflow so the shell can’t hold water.
- Give seepage an exit: Loosen or remove the drain plug so any weeping shutoff drips out, not back in.
- Skip open flame: Don’t torch plastic housings or near wiring. If you must warm anything, use controlled electric heat (hair dryer/heat tape) at a safe distance—slow and steady.
- Keep clear of electrical: If water is near outlets/panels, stay safe and wait for help.
What I do on arrival (my playbook)
- Isolate & depressurize the irrigation side, confirm main is safe.
- Vent the backflow fully (test cocks open), set a controlled drain path.
- Thaw safely if needed. If copper is a popsicle, I warm it carefully and away from plastic/rubber. (Pros have to read the materials and surroundings—no cowboy moves.)
- Evaluate damage: cracked shell, bent poppets/bonnets, distorted seats, split fittings.
- Save the season: even with a wrecked backflow, I can usually isolate/build a bypass for blowout and clear laterals/heads to mist so you don’t add a yard full of broken parts to the bill.
- Document everything on a paper Sprinkler Winterizing Report + text summary so spring repairs are straightforward.
Cost reality (straight talk)
Replacing a broken backflow is the big line item. But that’s only one component. If we act fast and properly blow out the rest, we often prevent dozens of smaller failures—cracked tall spray bodies, split elbows, shattered rotors—that turn a single part into a shopping list. In other words: the backflow is expensive, but not saving the rest is what really hurts.
Why big compressors win here (and why little ones burn out)
Every year I see curbside “FREE” compressors with a faint toasted smell. A big tank gives you seconds of air; winterizing needs minutes of steady CFM. I clear zones at modest 50–60 PSI with high volume so heads stay up, check-valves unseat, and we finish on a clean mist—and I don’t cook your parts (or my compressor).
Prevention next fall (5-minute checklist)
- Don’t just close #1 and walk away; schedule the blowout before hard freeze.
- Open test cocks at winterizing; confirm the shell vents.
- Leave the drain plug off/loose for 24–72 hrs so a weeping shutoff can’t refill the line.
- For tall sprays/side-inlets, make sure we ran to mist and cleared the “cup.”
- If you’re DIY: keep PSI modest, use short cool passes, and stop at mist.
Pipe Volume Cheat-Sheet (handy in a pinch)
- ¾″ PVC (ID≈0.824″): ≈ 2.8 gal / 100′
- 1″ PVC (ID≈1.029″): ≈ 4.3 gal / 100′
- 1″ poly (ID≈1.049″): ≈ 4.5 gal / 100′
- 1¼″ PVC (ID≈1.360″): ≈ 7.5 gal / 100′
Use it to visualize how much water we’re chasing to the nozzles before we hit mist.