FAQ
How to Read Your Backflow Test Results — What Does Pass or Fail Actually Mean?
When your certified backflow tester hands you (or emails you) a copy of the annual test report, the numbers and pass/fail notations can be confusing if you don’t know what you’re looking at. This guide explains exactly what the key measurements mean, how pass and fail thresholds work for each type of device, what specific failure modes look like on the report, and what your next steps are depending on the outcome.
For a general overview of what a test report looks like and where it gets filed, see our guide to what a backflow test report contains and how it’s submitted.
The Core Measurement: Differential Pressure
The fundamental measurement in any backflow preventer test is differential pressure — the difference in water pressure on either side of a check valve or relief valve, measured in pounds per square inch (PSI). This measurement tells you whether the valve is holding a seal under test conditions.
Think of a check valve as a spring-loaded door that opens in one direction and closes in the other. The spring provides a certain amount of resistance (measured in PSI). For the check valve to be considered functional, it must hold a specific minimum differential pressure — meaning the pressure on the upstream side must be able to exceed the spring resistance by at least the required minimum amount, and the valve must remain fully closed when pressure is applied from the downstream side.
Reading Pressure Vacuum Breaker (PVB) Test Results
A PVB test measures two things: the check valve differential pressure and the air inlet opening point. The check valve must hold a minimum differential pressure (typically ≥ 1.0 PSI) to pass. The air inlet must open when the upstream pressure drops to near atmospheric, allowing air to enter and break any potential siphon.
Pass: Check valve differential ≥ 1.0 PSI AND air inlet opens appropriately.
Fail — Low Check Valve Differential: A reading below 1.0 PSI means the check valve spring has weakened or the valve disc is not seating properly. This is the most common PVB failure mode. Typically resolved by replacing the check valve assembly with a rebuild kit.
Fail — Air Inlet Not Opening: The air inlet valve (bonnet assembly) has seized or its rubber element has hardened. The bonnet assembly requires replacement.
Reading Double Check Valve Assembly (DCVA) Test Results
A DCVA test measures the differential pressure across two separate check valves. Each must hold a minimum of 1.0 PSI differential to pass. The test report shows two readings: Check Valve #1 (upstream) and Check Valve #2 (downstream).
Pass: Both check valves ≥ 1.0 PSI differential.
Fail — One Check Valve Below Threshold: One check valve has weakened while the other remains functional. The failing valve’s disc and spring require replacement. With both check valves failing: both need service.
Reading Reduced Pressure Zone (RPZ) Test Results
RPZ testing is the most complex because three components are evaluated: Check Valve #1 (upstream), Check Valve #2 (downstream), and the Differential Pressure Relief Valve. The relief valve test is unique: it must open at a differential that is LESS than the differential held by Check Valve #1, and it must maintain a specific minimum differential pressure in the relief zone.
Pass: Check Valve #1 ≥ 2.0 PSI, Check Valve #2 ≥ 1.0 PSI, Relief Valve opens below CV#1 differential AND maintains ≥ 2.0 PSI in the relief zone. (Minimum values may vary slightly by model and authority.)
Fail — CV#1 Low: Most critical failure. Upstream check valve is not holding adequate differential. Requires immediate service — the primary protection is compromised.
Fail — Relief Valve Opens Too Late or Too Early: The relief valve is not calibrated correctly. It either won’t protect against a check valve failure (opens too late) or discharges excessively under normal operation (opens too early). Relief valve diaphragm or spring replacement typically resolves this.
Fail — Relief Valve Won’t Close: The relief valve is stuck open or discharging continuously. Often caused by debris on the seat or a deteriorated diaphragm. Requires service before the device can be certified.
What 'Repaired and Retested' Means on Your Report
When a device fails its initial test but is repaired during the same service visit and retested with a passing result, the report will typically show both the initial (failing) readings and the final (passing) readings after repair. The passing final test result is what satisfies the compliance requirement. This is the normal resolution pathway for most test failures — same-day repair is standard practice at South Jersey Backflow. See our guide to backflow preventer installation, testing, and rebuilding costs for typical repair pricing.
What to Do If Your Device Cannot Be Repaired on the Same Visit
Occasionally, a device failure requires parts that aren’t on the service vehicle, or the device’s condition is severe enough that a replacement decision is needed. In these cases, the failing test report is on record, the device is out of compliance, and a follow-up visit is needed within the compliance deadline to pass. This is the situation where you’ll want to read our guide on repair or replace your backflow preventer to make the right decision quickly. Contact South Jersey Backflow for prompt follow-up service throughout all of New Jersey.
Schedule Your Backflow Service Anywhere in New Jersey
South Jersey Backflow has proudly served residential and commercial customers across all of New Jersey since 2004. Our certified technicians provide annual backflow testing and certification, expert repairs and rebuilds, and protective backflow enclosures — all with transparent pricing, complete paperwork handling, and 24/7 emergency availability. Call (856) 291-6809 or contact us online to get started today.