The assembly has to be repaired or replaced, retested by a certified tester, and a passing report filed with your water provider by its deadline. Most failures are fixed by cleaning or rebuilding the check valves or relief valve. Mesa wants repairs done by the compliance date, and Scottsdale gives 45 days after its notice.
Step 1: Understand what failed
The tester's report will say which part didn't hold. On Phoenix's form, a failing report lists "the date of failure, date of repair, date passed," along with the tester's certification number, so the whole story ends up on one page.
For an RPZ, the troubleshooting table in the Ames 4000RP manual (Ames is a Watts brand) shows the usual suspects and the fix for each:
| What failed | Typical fix |
|---|---|
| First check fouled (debris on the seat) | Take it apart and clean the No. 1 check |
| Second check leaking, with backpressure from the building | Clean the No. 2 check and find what's causing the backpressure |
| Relief valve leaking through the diaphragm or around the bolt holes | Service the relief valve |
| Relief valve won't close | Service the relief valve |
| Discharge from pressure swings, not a bad part | Control the supply line pressure |
Notice what's missing from that list: "replace the whole assembly." Every fix is a cleaning or a service of one part. Replacement comes in when a part can't be repaired, which is exactly the case Gilbert's permit rule below is written for.
Step 2: Repair it, with the right person and paperwork
The repair has rules of its own:
- Who can repair. In Phoenix, repairs must be done "by a certified repairer" following ASSE Standard 5130 (City Code 37-143). Scottsdale limits installation, testing, repair and replacement to individuals "certified and approved by an agency recognized by the Division" (Revised Code 49-65).
- Permits for replacement. Phoenix's 2024 building code amendments exempt "repair or replacement of existing 2" and smaller secondary backflow prevention assemblies" from a permit, as long as a certified tester's report goes to the city (Sec. 105.2, plumbing item 6). But two current city documents point the other way. TRT 00634, updated in 2025, says replacing any backflow assembly needs a plumbing permit, and City Code 37-143 requires a permit "for the installation of any backflow prevention assembly." Assemblies on a fire line need permits from both Planning and Development and the Fire Department (TRT 00634). Until the city settles it, ask the Backflow Prevention Program at 602-534-2140 before you skip a permit. Gilbert requires a permit, with a fee, when a failed assembly "cannot be repaired" and has to be replaced.
- Parts on the record. Phoenix's report form asks the tester to list any replaced parts, with part numbers, in the comments.
Step 3: Retest and file the passing report
A repair isn't finished until a certified tester retests the assembly. Arizona's rule requires a test "after installation, relocation, or repair," and Mesa sets a clock on it: a recognized tester must retest "within 24 hours" after any overhaul, repair or replacement (City Code 8-1-11).
Then the passing report goes in. Surprise, for one, won't treat a failed test as a completed submission, so the passing retest is what clears you.
### Who pays, and what if water has to go off
The customer pays. Mesa says testing and servicing are "at the expense of the customer" (City Code 8-1-11), Scottsdale says testing and maintenance are "at the expense of the user" (Revised Code 49-65), and Tempe says repairs are made "at the customer's expense" (City Code 33-107). Between landlord and tenant, the lease should say who books and pays for the work.
A repair usually means shutting the assembly's valves, and on a main service that can cut water to the whole building. Plan the repair for off hours at a restaurant or clinic. Buildings that can't lose water at all are why Scottsdale requires two assemblies side by side when a user "requires a continuous water supply" (Revised Code 49-63). One stays in service while the other is repaired and tested.
Tempe adds one more step after a repair: the user must "have it inspected by the department and tested by a certified tester" (City Code 33-107). Ask your tester whether your provider needs an inspection before it will take the passing report.
### When the same assembly keeps failing
A repeat failure usually means the cause is outside the valve. Watts's 009 manual says a new assembly can discharge because of "inadequate initial flushing of pipe lines to eliminate dirt and pipe compounds," so debris from new work is worth ruling out. The Ames 4000RP troubleshooting table says a leaking second check with backpressure calls for finding "the cause of back pressure," not just cleaning the check again.
Sometimes the device is simply the wrong type for the spot. Glendale makes testers run a backpressure check on every pressure vacuum breaker. If the PVB turns out to be subject to backpressure, Glendale's policy calls it "improperly installed" and the tester marks it failed. Mesa's code points the same way: where a PVB "cannot be at least 12" higher than all downstream plumbing," an RP is required instead (City Code 8-1-8). In those cases, rebuilding the PVB won't help. The fix is the right assembly, with a permit.
How long you have in each city
| Provider | Repair deadline after a failed test | Source |
|---|---|---|
| Mesa | By the compliance due date. A failure found between annual tests gets 15 calendar days. Retest within 24 hours; records within 7 days | City Code 8-1-11 |
| Scottsdale | 45 days after the city's notice; records within 7 days | Revised Code 49-65 |
| Phoenix | Repair by a certified repairer; the city can act under City Code 37-146 if an assembly isn't maintained | City Code 37-143, 37-146 |
| Gilbert | Replacement permit required when a failed assembly can't be repaired | Gilbert Backflow FAQ |
Don't let a failed assembly sit. Phoenix can shut off water for failing to "maintain a required backflow prevention assembly," and a broken assembly protects nothing in the meantime. Fire line assemblies follow the same idea, but they're fire system work. In Phoenix, the tester must also be permitted by the City Fire Marshal (City Code 37-143), and replacing one takes Fire Department permits (TRT 00634).
Save time on the next test
A few habits cut down on repeat failures. Ask the tester what they found inside, not just "pass" or "fail." If the same check keeps fouling, look upstream for the cause, like debris after main work or pressure swings. And keep the repair paperwork with the test report; Phoenix requires you to keep testing records for at least three years.
If your RPZ is dumping water between tests, why an RPZ backflow preventer spits water explains the causes. For report deadlines by provider, see where to send backflow test reports in the Phoenix area. And if the deadline has already passed, read what happens if you miss a Phoenix backflow test deadline.
HQ Plumbing & Air repairs and replaces failed backflow assemblies on domestic water and irrigation lines, then retests them so the passing report can go in. Upfront pricing before any parts go in.