To test a backflow prevention device, you must use a calibrated differential pressure gauge to verify that check valves and relief valves operate correctly under simulated backpressure or backsiphonage conditions. This guide explains how to test a backflow prevention device safely and in compliance with US plumbing codes, helping you protect your home's potable water supply from contamination.
What Is a Backflow Prevention Device?
A backflow prevention device is a mechanical assembly installed on your water line to stop contaminated water from flowing backward into the public water supply. Common types include the Pressure Vacuum Breaker (PVB), Reduced Pressure Zone (RPZ) assembly, and Dual Check Valve. Regular testing is required by most municipalities to ensure these devices function correctly.
Why Testing Matters
Backflow can introduce chemicals, bacteria, or sewage into your drinking water. The EPA WaterSense program emphasizes that cross-connections are a major health risk. Annual testing by a certified tester is often legally required. Without proper testing, you risk fines, health hazards, and voided warranty coverage.
Step-by-Step: How to Test a Backflow Prevention Device
Only a certified backflow tester with a valid state license should perform these tests. The following outlines the standard procedure for an RPZ assembly, the most common device in commercial and residential settings.
Tools You Will Need
- Calibrated differential pressure gauge (with current calibration certificate)
- Test kit hoses and fittings (typically 1/4-inch)
- Small flat-head screwdriver
- Bucket or towel (for minor water spillage)
- Safety glasses and gloves
Step 1: Visual Inspection
Check for leaks, corrosion, debris, or signs of tampering. Ensure shut-off valves are open and the device is not frozen or damaged. Any visible defects must be repaired before testing.
Step 2: Attach the Test Kit
Connect the pressure gauge hoses to the test cocks on the device. The RPZ has three test cocks: #1 (upstream of first check valve), #2 (between first and second check valves), and #3 (downstream of second check valve). Attach the high side of the gauge to test cock #2 and the low side to test cock #3 for the first test.
Step 3: Test the First Check Valve
Close test cock #2 and open test cock #4 (if present) or use the bleed valve. Slowly open the bypass valve (if equipped) to simulate backpressure. The gauge should indicate a pressure differential of at least 5 psi. If the reading drops below 5 psi, the first check valve is leaking.
Step 4: Test the Second Check Valve
Reposition the gauge with the high side on test cock #1 and low side on test cock #2. Close test cock #1 and open the bleed valve. The differential should again be at least 5 psi. If not, the second check valve is faulty.
Step 5: Test the Relief Valve
With the gauge still connected, slowly close the downstream shut-off valve while monitoring the relief valve opening. The relief valve should open when the pressure in the zone drops to approximately 2 psi below the supply pressure. If it fails to open or leaks during normal operation, the relief valve needs replacement.
Step 6: Record Results
Document all gauge readings, device model, serial number, test date, and tester certification number. Submit the test report to your local water authority as required.
Common Test Results and What They Mean
| Test Result | Possible Cause | Action Needed |
|---|---|---|
| First check valve fails (differential <5 psi) | Worn rubber seal, debris on seat | Rebuild or replace first check assembly |
| Second check valve fails (differential <5 psi) | Corrosion, damaged spring | Rebuild or replace second check assembly |
| Relief valve does not open | Stuck diaphragm, blocked port | Clean or replace relief valve |
| Relief valve leaks continuously | Debris, worn seat | Flush device; if persists, replace valve |
When to Call a Professional
If you notice low water pressure, sputtering faucets, or discolored water after a backflow test, contact a licensed plumber immediately. Attempting repairs without proper training can cause cross-contamination. MyTownPlumber offers water heater repair and drain cleaning services alongside expert backflow testing and maintenance. For hidden leaks that may affect test results, our leak detection team can help.
Local Codes and Certification
Most US states require backflow testers to hold a certification from an approved organization such as the International Association of Plumbing and Mechanical Officials (IAPMO). Test frequency varies: annual testing is typical for RPZ assemblies, while PVBs may require testing every 6–12 months. Check with your local water utility for specific requirements.
Frequently Asked Questions
How often should a backflow prevention device be tested?
Most municipalities require annual testing. However, commercial properties or high-hazard applications (e.g., irrigation systems with chemical injectors) may need testing every 6 months. Always verify with your local code enforcement office.
Can I test my own backflow preventer?
Only a certified backflow tester with a valid state license can legally perform a test that satisfies local code requirements. DIY testing is not recognized by water authorities and may result in fines.
What happens if a backflow test fails?
The device must be repaired or replaced by a qualified plumber. After repairs, a retest is required to confirm compliance. Your water utility may shut off service until the device passes.
How much does a backflow test cost?
Typical costs range from $75 to $150 for a standard residential test, but prices vary by region and device type. Commercial or large-diameter assemblies may cost more. Always request a quote before service.
What is the difference between an RPZ and a PVB?
An RPZ (Reduced Pressure Zone) assembly provides the highest level of protection and is used for high-hazard applications. A PVB (Pressure Vacuum Breaker) is suitable for low-hazard irrigation systems but does not protect against backpressure.
Will a backflow test affect my water pressure?
During the test, water may be briefly shut off or flow reduced. Normal pressure returns immediately after the test is complete. If low pressure persists, there may be an underlying issue such as a clogged line.
Protect Your Water Supply Today
Regular backflow testing safeguards your family and community. MyTownPlumber provides certified testing and repairs throughout the US. Pipe repair and sump pump services are also available for related plumbing needs. For a limited time, new customers receive a special offer on backflow testing. Click here to claim your discount.
— MyTownPlumber Editorial Team