Water discharging from the relief port
A check valve has failed and the relief is doing its job. Plugging the discharge is dangerous and defeats the purpose of the device entirely.
Backflow testing in Sonoma State University, CA, with the gauge readings recorded and the paperwork filed
Certification falls due once a year on a fixed date. Let it slip and the authority writes to you; let the device fail and the supply itself is at risk.
Backflow prevention is the least visible plumbing work in any building and the only part of it with a public health rationale behind it. The assembly exists to stop water flowing backward from a property into the public supply, which matters because whatever is in that property's system, whether irrigation water, boiler treatment chemicals or process fluid, would otherwise have a path into everyone else's drinking water.
Because it protects against something that almost never happens, and because it sits in a closet or a pit, it gets ignored. The device fails quietly, the annual test date passes, and nothing appears to be wrong until a notice arrives from the water authority or until a pressure event actually occurs.
What the test involves
A calibrated differential pressure test kit connected to the assembly test cocks, the check valves and the relief valve each verified against the required differential, the readings recorded on the authority form, and the certification submitted. Roughly half an hour on a compliant device, longer where something has to be rebuilt.
- Calibrated test kit, with its calibration date on the report
- Each check valve verified against the required differential
- Relief valve opening point tested on reduced pressure assemblies
- Results filed on the form the authority actually requires
AnnualTesting interval required on most assemblies
FiledCertification submitted, not left with you to send
CalibratedTest kit with current calibration, noted on the report
RecordedEvery differential reading written on the form
RebuiltFailed checks and relief valves repaired in place
SubmittedPaperwork filed with the authority for you
What the assemblies do and where they are
Four common device types, each protecting against a different level of hazard.
A reduced pressure zone assembly is the highest level of protection in common use. It contains two independent check valves with a relief valve between them, and if either check fails the relief opens and discharges to atmosphere rather than allowing backflow. That discharge is by design, and a reduced pressure assembly that is dumping water is telling you a check has failed rather than that the relief valve is broken.
A double check valve assembly has two checks in series and no relief. It is used where the hazard is lower, typically on fire sprinkler systems and on some irrigation installations. It is less tolerant of failure than a reduced pressure assembly because there is no visible sign when one check stops sealing, which is precisely why the annual test matters.
Pressure vacuum breakers and atmospheric vacuum breakers are used on irrigation systems and protect against back siphonage rather than back pressure. They are simpler, they sit above the highest outlet, and they have their own installation requirements about height that are frequently not met on systems fitted by landscapers rather than plumbers.
Where they appear is fairly consistent. Irrigation systems, fire sprinkler supplies, boiler fill connections, commercial kitchens, medical and dental premises, car washes and any property with a secondary water source all typically require one. The boiler fill connection is the one most homeowners have without knowing it, and it is also the device that most often causes the thermal expansion complaints that show up at the water heater.
What the report contains
The record that satisfies the authority and gives you something to compare against next year.
- Device type, make, model, size and serial number
- Differential readings for each check valve and the relief where fitted
- Test kit identification and its current calibration date
- Pass or fail, and details of any repair carried out to achieve a pass
Signs an assembly needs attention
Six indicators, several of which are commonly mistaken for something else.
Backflow devices give limited warning, which is the whole reason for a scheduled annual test rather than a reactive approach. The signs below are what does show up.
The discharging relief valve is the one most often misread, because it looks like a fault in the relief valve rather than a report about the checks.
Notice received from the water authority
The test date has passed. These escalate, and in some jurisdictions an unresolved notice can lead to the supply being restricted.
Relief valve weeping intermittently
Often debris on a check seat rather than outright failure. Frequently repairable by rebuilding rather than replacing the assembly.
Pressure complaints elsewhere in the building
A backflow device makes a system closed, which is the usual cause of thermal expansion pushing a water heater relief valve open.
Assembly visibly corroded or leaking at a fitting
Common on external installations that have been through several winters without being drained or protected.
Device installed below the required height
Applies to vacuum breakers on irrigation. A non compliant installation fails its test regardless of the condition of the internals.
How a test visit runs
Six steps, about half an hour where the device passes.
Testing isolates the supply through the assembly briefly, so where that matters, on a commercial site or an irrigation system in use, it is scheduled for a convenient time rather than turning up unannounced.
Identify and record the device
Type, make, model, size and serial captured, because the authority record has to match the physical device.
Visual inspection
Installation orientation, clearances, drainage for the relief port and general condition checked before any gauge is connected.
Connect the calibrated kit
Test cocks opened and the differential gauge connected, with the kit calibration date recorded on the report.
Test each element
Both check valves verified against the required differential, and the relief valve opening point tested where the assembly has one.
Rebuild if it fails
Worn seats, discs and springs replaced using the manufacturer repair kit, in place, and the assembly retested to confirm a pass.
Submit the certification
Paperwork completed and filed with the authority, with a copy for your records and a reminder for next year's date.
Repair in place rather than replace
Most failed assemblies do not need replacing, and the difference in cost is substantial.
A backflow assembly is a body with serviceable internals. When it fails a test, the cause is almost always a worn rubber disc, a scored seat, a tired spring or debris lodged where it should not be. Every reputable manufacturer produces a repair kit containing exactly those parts, and fitting one restores the device to specification.
Replacement is the easier sell and it is occasionally necessary. A cracked body, a device so corroded that the internals cannot be removed without damage, or an obsolete assembly with no kit available all genuinely need replacing. Those are identifiable conditions rather than default outcomes, and where one applies you get shown why.
The other case for replacement is a non compliant installation. An assembly fitted at the wrong orientation, without the clearances required for testing and servicing, or below the required height for its type will fail its test regardless of condition. Correcting that is installation work rather than a repair, and it usually comes up on systems fitted by somebody who was not a plumber.
When replacement is genuinely required
- Cracked or corroded body that cannot be made watertight
- Internals seized to the point that removal would damage the seats
- An obsolete assembly with no manufacturer repair kit available
- An installation that cannot be made compliant in its current position
- Freeze damage, which is common on unprotected external assemblies
Backflow testing questions
Who needs it, how often, what a failure means and what happens to the paperwork.
If you have a testable assembly on your service, in most jurisdictions yes, and the requirement sits with the property owner rather than with the water authority. The interval is usually annual and the date is tied to the device rather than to the calendar year.
Properties with irrigation systems, fire sprinklers, boiler fill connections or any commercial process water use are the common cases. If you are unsure whether you have one, it can be identified during any other visit.
It gets repaired and retested, usually on the same visit. Most failures are worn internals and the manufacturer repair kit restores the device to specification, after which it is tested again and the pass is recorded.
Where it cannot be repaired, that is explained with the reason. The authority generally allows a defined period to resolve a failure, so a failed test is a task rather than a crisis provided it is acted on.
We do. The completed test report goes to the authority as part of the job rather than being handed to you to deal with, and you get a copy for your records.
You also get a note of when the next test is due, because the date follows the device and missing it is the most common way properties end up with a notice.
No, and this is the one item on this page where the answer is absolute. The relief port is the safety function of the device. Capping or plugging it removes the protection entirely and leaves you with an assembly that looks compliant and is not.
A dripping relief is reporting that a check valve is not sealing. That is repairable, usually inexpensively, and it should be repaired rather than silenced.
Briefly, for the few minutes the assembly is isolated. On a domestic property that is rarely an issue. On a commercial site or a property with a process that cannot tolerate an interruption, it gets scheduled for a suitable time.
Irrigation assemblies are usually tested when the system is being commissioned for the season, which avoids any interruption at all.
It gets assessed, because freeze damage frequently cracks the body rather than merely damaging the internals. Where the body is sound, a rebuild restores it. Where it is cracked, it needs replacing.
The more useful conversation afterwards is prevention: draining the assembly for winter where the type allows it, or fitting an insulated enclosure. Replacing the same device every few winters is an avoidable expense.
Get the annual test booked before the date passes
Testing and certification in Sonoma State University, CA, with the paperwork filed rather than handed to you.
Call with the type of property and what the device protects if you know: irrigation, fire sprinkler, boiler fill or process water. If you are not sure what you have, the device can be identified on site.
If you have already received a notice from the water authority, mention it and bring the date. That determines how quickly the test needs to happen and what the authority is expecting.