Why did my backflow preventer fail its test?

A backflow preventer usually fails its test because an internal check valve or relief valve no longer seals. Dirt or debris on a rubber seat, worn or hardened rubber parts, and freeze damage are the common causes. A failed test is not a verdict that you need a new device: an assembly is repairable in line.^[2] A certified tester or plumber repairs or replaces it, and it has to pass a re-test before the paperwork counts.

What a failure means

The test gauge measures how well the assembly's internal valves hold. Chesterfield County's irrigation guide says a pressure vacuum breaker must be overhauled or replaced if tests reveal the check valve closes at less than 1.0 psi (pounds per square inch) on the test gauge.^[1] For a reduced pressure assembly it says the assembly must be overhauled or replaced if tests reveal the check valves will not hold tight or the relief valve opens at less than 2.0 psi on the test gauge.^[1] Your test report tells you which reading failed, and that points to the repair. If you do not know which type you have, what a backflow preventer is and how it is tested explains the difference.

Common reasons an assembly fails

Debris on a check valve seat. A grain of grit, a bit of pipe scale or a sliver of plastic from installation can hold a check valve slightly open. Cleaning the seat can be enough, and the tester will tell you if it is.

Worn rubber parts. Seats, discs and diaphragms stiffen and wear. Chesterfield's guide says the assembly should be overhauled (replacement of internal parts as a minimum) every five years,^[1] and notes that the manufacturer recommends that the backflow prevention assembly be overhauled on the same schedule.^[1] An assembly that has gone many years without new parts is a likely failure.

Freeze damage. Chesterfield lists "Must be protected from freezing" for both common assembly types.^[1] A cracked body or split fitting shows up as water leaking after the system is turned on in spring. Its guide suggests a freeze-resistant model or an approved insulated enclosure, and also says the assembly cannot be wrapped with insulation.^[1] Wrapping it in rags or foam is the wrong fix.

Damage and poor installation. A mower strike, a cracked test cock or a leaking relief valve can all fail a test. So can installation that does not meet the rules. The guide says a pressure vacuum breaker must be installed a minimum of 12 inches above the highest downstream outlet,^[1] a reduced pressure assembly a minimum of 12 inches above grade,^[1] and either one has to be accessible for testing and maintenance.^[1] A pressure vacuum breaker must also be installed upright (air inlet canopy at top).^[1] If a new landscaping bed has buried the assembly, or sprinkler heads have been added higher than the device, that is an installation problem, not a worn part.

A blow-off in the wrong place. The same guide says the pipe used for blowing out the system with air is not allowed upstream (before) the backflow prevention assembly.^[1] If your system has one ahead of the device, tell the tester.

What happens after a failed test

Expect a repair quote or a replacement quote, then a re-test. In Fairfax County the assembly must be repaired or replaced, and re-tested before a Backflow Assembly Test Report can be submitted by the vendor.^[2] The county also says it will not accept a partial report: Fairfax County will NOT accept partial or incomplete Backflow Assembly Test Reports.^[2] If the assembly needs replacing, the same county page says that work requires a Plumbing Permit.^[2] Localities differ, so ask your tester or utility what yours requires and who files the report. For the rules and deadlines, read whether Virginia requires annual backflow testing.

Ask the tester for the failed reading, what they found inside, and a written price for repair and for replacement. Repair may cost less than replacement for a device that is otherwise sound, but a cracked body or an old, obsolete model may not be worth rebuilding. For what drives the price, see how much backflow testing costs in Virginia.

When to call a licensed pro

For the repair, the re-test and any replacement. Testing and repair of these devices are regulated work, and replacement may need a permit. The state's tradesman rules define a backflow prevention device worker as someone who engages in, or offers to engage in, the maintenance, repair, testing, or periodic inspection of cross connection control devices.^[3] Chesterfield County states that individuals who perform tests on backflow prevention assemblies must hold a valid Tradesman Certificate as a Backflow Prevention Device Worker issued by the Virginia Department of Professional and Occupational Regulation.^[1] You can check the tester's certification on DPOR's License Lookup before you book.^[4]

Do not open the assembly, adjust it or try to clear it yourself. Call a certified tester or licensed plumber when:

• A test report says the assembly failed. It needs repair or replacement and a passing re-test.
• Water sprays or drips from the relief valve or body. Shut off the irrigation supply and book a visit.
• The device was hit, frozen or flooded. Damage you cannot see can still fail a test.
• You are not sure the device is installed correctly, for example it sits in a pit, is buried or is lower than the sprinkler heads.

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