Every spring in Northern Virginia, the same story plays out at thousands of houses: the backflow test that should have been a routine pass turns up a cracked device, because water sat inside it all winter and froze. It’s the single most common reason backflow preventers fail their annual test around here, and it is almost entirely preventable with an hour of work in the fall. Here’s what to do before the first hard freeze, which in our area usually means getting it done by late October.
Why freezing kills backflow preventers
The PVB on a typical home irrigation system lives above ground, on purpose, up where it can do its job. That also leaves it exposed. Water trapped inside the valve body expands as it freezes, and the brass and plastic internals lose that fight every time. The crack is usually invisible from the outside. The device looks fine all winter, then fails the gauge test in the spring, and now your routine test comes with a replacement attached.
Winterizing, in the right order
- Shut off the irrigation supply. There’s a dedicated shutoff for the sprinkler line, usually in the basement or a utility area, downstream of your main.
- Drain or blow out the system. Gravity drains handle some systems; most around here get a compressed-air blowout so no water sits in the lines or the device. Blowouts want the right pressure and some care, so if you don’t own a compressor and a reason to love this job, it’s a quick visit for a pro.
- Leave the device ready for winter. Isolation valves and test cocks get set partway open (about 45 degrees) so no chamber traps water, and an insulated cover adds cheap protection for the device itself.
Two local rules that surprise people
- Loudoun Water: remove it, retest it. Some homeowners take the PVB off entirely and store it inside for the winter, which is great for the device but comes with a rule: Loudoun Water requires any irrigation backflow device that was removed for winterization to be retested when it’s reinstalled. Leaving it in place, drained and covered, avoids the extra test.
- Prince William County: antifreeze means RPZ. If your irrigation company winterizes with antifreeze rather than air, county code approves exactly one backflow device for that setup, an RPZ (ASSE 1013). A PVB plus antifreeze is a code problem hiding in plain sight.
What this buys you in April
When the notices start arriving in spring, a winterized system means your test is just a test: 30 minutes, a passing report, done for the year. A skipped winterization is how a small line item becomes a device replacement. If you want the full picture of what your utility requires, deadlines included, our backflow service page lays out every Northern Virginia program in one place.
Want it handled? We winterize irrigation backflow setups, repair freeze-damaged devices, and run the annual tests when they come due. Call (703) 997-9757 or book online before the first freeze beats you to it.
