Updated October 28, 2026
A backflow preventer is a one-way door that keeps sprinkler or boiler water from running back into the water lines. When it breaks, one of two things happens: it leaks water you can see, or it stops doing its job and you can’t see anything at all. In Northern Virginia the yearly backflow test catches the second kind, and ours is $250, normally $300, on our backflow testing page.
If a screen door’s spring snaps, the door still looks like a door. It just doesn’t close anymore. A broken backflow preventer is a lot like that. Here’s what breaking looks like, what it costs you while it’s broken, and how it gets fixed.
What a broken backflow preventer looks like
These are the signs, from loud to quiet:
- Water spraying or pouring out, usually from a crack in the body or from the bottom of an RPZ.
- A steady drip from an RPZ’s relief valve, the opening on its underside.
- A soggy mulch bed or a wet spot in the yard around an outdoor device that won’t dry out.
- A crack or a bulge in the brass after a cold night.
- A weak lawn sprinkler while the faucets inside are fine.
- Nothing at all, and a failed test. This is the most common kind, because the parts that wear out are inside.
For more warning signs, see signs of a backflow problem. If you’re not sure what the device even is, start with what a backflow preventer does.
Why a broken RPZ backflow preventer dumps water
An RPZ, short for reduced pressure zone, is built to leak on purpose when something’s wrong. Virginia’s waterworks definitions describe it as two spring-loaded check valves with a relief valve between them. If either check stops sealing, the relief valve opens and dumps water out the bottom so nothing can sneak back toward the street.
So a dripping or pouring RPZ is a warning light, not the problem itself. The real problem is a check valve inside that isn’t closing, usually a tired spring, a worn rubber seal or grit stuck in the seat. A quick spit when the water pressure changes can be normal. A steady stream isn’t.
All the leak causes, device by device: what a leaking backflow preventer means.
$250 Yearly Backflow Test
The yearly test your water utility or county asks for, on a home's backflow preventer up to 1 inch. About backflow testing
A freeze-cracked backflow preventer: the break we see most
Most backflow preventers on houses here sit outside on the lawn sprinkler line. If water is left inside one on a hard freeze, it turns to ice, ice needs more room than water, and the brass body or the parts inside crack. A freeze-cracked pressure vacuum breaker, or PVB, is the break our plumbers see most.
Sometimes the crack is obvious and sprays the first time the sprinkler runs in spring. Sometimes it’s hair-thin and only shows up as a failed test. Loudoun Water says a device that was removed for winter gets retested once it goes back on, and that’s why.
What a broken backflow preventer costs you while it leaks
Here’s the part people miss: every gallon that runs out of a leaking backflow preventer already went through your water meter. You pay for it, whether it watered the lawn or ran down the curb.
- Outside, a spraying or dripping device soaks the bed around it, washes out mulch and can leave a soft, muddy patch by the foundation.
- Inside, an RPZ needs a drain under it for exactly this reason. If the drain can’t keep up with a pouring relief valve, the water ends up on the basement floor.
- On the sprinkler, a device that’s stuck partly shut leaves the heads weak, so the lawn gets less water while you still run the system as long.
Pressure problems have their own post: backflow and water pressure.
The leaks are a hassle. The broken check you can’t see is the bigger deal, because it means the one-way door isn’t one-way anymore.
Lawn sprinkler water can carry fertilizer and weed killer. Loudoun Water warns it can become contaminated from lawn care chemicals and get siphoned back through the sprinkler heads when the pressure in the main drops, like during a water main break or hydrant flushing. A working device closes. A broken one might let that water slide back toward your kitchen tap and the houses around you.
That’s the reason for the yearly test: why backflow testing is required every year. The basics of backflow itself: what backflow is in plumbing.
What to do right now about a broken backflow preventer
- Stop the water. Every testable device has a shutoff valve at each end. Turning the handle on the side the water comes from, a quarter turn so it sits across the pipe, stops the flow through it. On many sprinkler lines there’s also a shutoff in the basement where the line leaves the house.
- Don’t run the sprinkler until it’s fixed.
- Take a photo of the device and any tag on it. It helps us bring the right parts.
- Call us at the number below, or book online.
Don’t try to patch a crack with tape or sealant. A patched device won’t pass the test, and the test is what your water supplier cares about.
How a broken backflow preventer gets fixed
There are two ways to fix one:
- A repair kit. New springs, rubber seals and seats inside the same brass body. That’s usually the answer for a failed test on a device that isn’t cracked or corroded.
- A new device. For a cracked body, heavy corrosion, or when your water supplier asks for a different kind than the one you have. A new residential backflow preventer up to 1 inch runs $800 to $1,200, installed and tested.
Either way, Virginia wants it tested right after the repair or install. Loudoun Water wants a failed device fixed and retested within 30 days of its notice, with replacements done by a master plumber, and Fairfax County wants it within 10 business days of the failed test. With us, you get a written quote before any repair starts.
Finding the break with a backflow test
When nothing shows from outside, the gauge is how you find the break. The test reads each one-way door and the relief valve, so a failed test says exactly which part let go. That turns “something’s wrong” into a specific fix.
The steps: what happens during a backflow test. Test or inspection: the difference. Price breakdown: backflow test cost. If the yearly date already slipped: what happens if you skip a backflow test. Local pages: Fairfax County, Loudoun County, Prince William County, Chantilly, Annandale, Sterling and Haymarket.
Why SwiftPro makes a broken backflow preventer easy to sort out
Broken or just due, it goes the same way:
- Pay $250 online, normally $300. Or call (703) 997-9757, or book a time online, whichever you like.
- We call you to pick the day. Tell us where the device is and whether the sprinkler is shut down for winter, and keep your notice handy.
- We test it and tag it. A SwiftPro plumber hooks the gauge to the device, reads every check and writes the numbers down.
- We send the report where your water supplier wants it. Loudoun Water, Fairfax County, Prince William Water and the town programs each take it their own way, and yours goes in the way your notice asks.
- If it fails, you get a written quote before any repair. Nothing gets fixed until you say yes, and the device is tested again once it is.
All the details are on our backflow testing page.
Broken backflow preventer questions
How do I know if my backflow preventer is broken?
Water spraying or dripping from it, a soggy spot around it, a crack after a freeze, a weak sprinkler, or a failed test. Often there’s no sign at all, which is why it’s tested every year.
Why is my RPZ dripping from the bottom?
That’s the relief valve. It opens and dumps water when one of the check valves inside isn’t sealing. A quick spit when pressure changes can be normal; a steady drip or stream means it needs repair.
Is a broken backflow preventer dangerous?
It can be. If a check inside isn’t sealing, sprinkler water carrying lawn chemicals can get pulled back toward the water lines when street pressure drops.
Can a freeze break a backflow preventer?
Yes. Water left inside freezes and cracks the brass body or the parts inside. Freeze-cracked outdoor PVBs are the break we see most.
Can a broken backflow preventer be repaired?
Often, with a repair kit of new springs and rubber. A cracked or badly corroded body gets replaced. You get a written quote before any repair.
How much does it cost to replace a backflow preventer?
A new residential backflow preventer up to 1 inch runs $800 to $1,200, installed and tested.
Does a broken backflow preventer need to be retested after the fix?
Yes. Virginia wants every device tested right after a repair or install, and the passing report goes to your water supplier.
Get a broken backflow preventer fixed
Call (703) 997-9757, book online or use the form at the top of this page. If it’s just due for its yearly test, pay $250 online and we’ll call to pick the day. Everything is on our backflow testing page, the rest of our plumbing work is on our plumbing page, and current deals are on our offers page.
SwiftPro Heating, Cooling & Plumbing tests, repairs and replaces backflow preventers, water heaters, sump pumps and water and drain pipes, and services furnaces, heat pumps and air conditioners, across Northern Virginia from Chantilly and Ashburn, with a separate plumbing team and a dedicated HVAC team. Family owned, BBB Accredited with an A rating, 24/7 emergency service, Virginia Class A contractor license 2705192276, and rated 5.0 stars across 1,130 reviews on Google, Angi, Yelp, the BBB and Facebook. Read the reviews.
