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Fix a backflow that will not pass test

We'll check for leaks, flush debris, and rebuild or replace—or tell you when to call a licensed backflow tester.

Troubleshooting · Home maintenance
30–60 min
What you'll need
  • Backflow rebuild kit (if rebuilding)
  • Wrenches and screwdrivers
  • Replacement backflow (if needed)
Step 1 of 5

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Steps

Goal: Confirm the fault, then flush, rebuild, or replace.

Flush the backflow

Goal: Clear debris that may hold valves open.

  • Shut off the supply. Open the test cocks one at a time and flush. Open the relief valve manually if possible. Close all and retest.
  • Good: Passes after flush. Have it certified if required.
  • Bad: Still fails—proceed to Rebuild or replace.

Rebuild or replace

Goal: Replace worn seals and springs, or replace the unit.

  • Shut off the supply and drain. Disassemble per the manufacturer instructions. Replace worn parts with a rebuild kit. Reassemble and retest.
  • Good: Passes after rebuild.
  • Bad: Still fails—replace the unit or call a licensed backflow tester.

When to get help

Call a licensed backflow tester if:

  • The unit fails after flush and rebuild.
  • You need certification.
  • Your area requires a professional for testing and repair.

Do not bypass the backflow preventer—it protects drinking water.

Verification

  • Backflow passes the annual test.
  • No leaks at body, test cocks, or relief valve.
  • Certified by a licensed tester if required by your jurisdiction.

Escalation ladder

Work from the device outward. Stop when the problem is fixed.

  1. Confirm fault Get the test report; know which component failed.
  2. Flush Flush debris through test cocks and relief valve.
  3. Rebuild Replace seals, springs, and worn parts.
  4. Replace Replace the entire unit if rebuild fails.
  5. Call a pro Licensed backflow tester for certification or complex repair.

What to capture if you need help

Before calling support or posting for help, have these ready. It speeds everything up.

  • Test report and failed component
  • Backflow type and model
  • Steps already tried

Did the backflow fail its test?

Get the test report. It will state which component failed.

Review the test report. Good: specific fault (check valve, relief valve)—proceed to fix. Bad: no report—have it retested to get the fault.

Yes No

You can change your answer later.

Did flushing fix the failure?

Debris can hold valves open. Flush through test cocks.

Shut off supply. Open test cocks and flush. Open relief valve to flush. Retest. Good: passes after flush. Bad: still fails—rebuild or replace.

Yes No

You can change your answer later.

Did rebuild fix the failure?

Worn seals and springs cause failure. Rebuild kit replaces them.

Shut off supply. Disassemble per manual. Replace seals and worn parts. Reassemble. Retest. Good: passes after rebuild. Bad: still fails—replace unit or call a pro.

Yes No

You can change your answer later.

Backflow passing

The backflow preventer should now pass the test. Have it certified by a licensed tester if required.

Done

Call a pro

Call a licensed backflow tester if the unit fails after rebuild, you need certification, or your area requires a professional. Do not bypass the backflow.

Done

Reviewed by Blackbox Atlas

Frequently asked questions

Why would a backflow fail its test?
Common causes: leaking check valves or relief valve, debris holding valves open, worn seals or springs, or improper installation. The inspector will specify the fault.
Can I fix a backflow that will not pass test myself?
You can flush debris and check for leaks. Rebuilding or replacing internal parts often requires a licensed backflow tester. Many jurisdictions require a certified professional for testing and repair.
When should I call a pro for a backflow?
Call a licensed backflow tester if the unit fails inspection, you need a rebuild, or your area requires certified testing. Do not bypass or remove a backflow—it protects drinking water.

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