Failed backflow test: what happens next

What “failed” actually means

The annual test measures whether each moving part of the assembly still holds against reverse flow at or above the minimum values in CSA B64.10.1. A failure means at least one of them did not:

Assembly	Fails when
DCVA	Check 1 or check 2 leaks or holds below the minimum differential; a shut-off valve will not hold so the test cannot be completed
RPZ	Relief valve opens late or not at all; relief valve discharges continuously; check 1 or 2 leaks or holds below minimum
PVB	Air inlet does not open at the required differential; check leaks or holds below minimum

A device can fail on one component and be otherwise sound. That matters for the repair.

Why devices fail

The boring reasons, which is good news because boring is fixable:

• Debris on a check disc. Scale, grit, sediment after a main break or nearby construction. The disc cannot seat. Sometimes a flush clears it; usually the disc is scored and needs replacing.
• Worn rubber. Discs, seats and O-rings harden and crack over years of cycling. Standard rebuild.
• Weak springs. The check no longer closes with enough force to hold the minimum.
• Relief valve trouble (RPZ). A weeping relief valve almost always means the first check is marginal. A relief valve that will not open means a stuck diaphragm or blocked sensing passage, which is the dangerous one.
• Stuck air inlet (PVB). The device sat idle over winter, the poppet dried in place. The most common irrigation failure.
• Freeze damage. Cracked bonnets and bodies from water left in the device in an unheated space or an unwinterised irrigation line.
• Shut-off valves that will not hold. The assembly may be fine, but if the tester cannot isolate it, it cannot be proven fine. Old gate valves are the usual culprit.

Our device pages go deeper: DCVA, RPZ, PVB. Hard water and its effect on seats and springs is covered in why backflow preventers fail.

What the by-law requires when a device fails

Section 6.4 of By-law 24-2018 is short and specific. If a test shows the device is not in proper working condition, the authorized tester:

1. Provides written notification to the Region and the area municipality within twenty-four (24) hours. This is the tester’s duty, not yours. We do it as part of the visit.
2. Immediately makes all necessary repairs or replaces the device, at the expense of the owner. “Immediately” is the by-law’s word. Repairs are plumbing work, so this means a licensed plumber promptly.

Two related rules: a device may not be by-passed without the Commissioner’s authorization (section 6.7), and it may not be removed except to replace it with an equal or better device, with the water off while it is out (section 6.8). So the fix is repair-in-place or straight replacement, never “take it out for now.”

Who does the repair

Appendix A of the by-law lists who may perform each function. Testing (row D) is open to anyone with a tester’s licence. Repair (row C) is restricted to licensed plumbers, engineers and technologists with a tester’s licence, plus in-house maintenance staff and water operators who hold one. Installing or replacing a device (row B) is plumbers only.

That is why the honest answer to “can you fix it while you are here” is usually no. We coordinate the repair with a licensed plumbing partner, agree the scope and price with you first, and schedule the retest to follow. If your building already has a plumber you trust, they can do the repair and we still handle the retest and filing.

The retest and the filing

After the repair, the device is tested again from the start, all components, and a new report is submitted through BSI Online. The Region reviews the passing report and the compliance record closes. You get the tag, the report copy for your five-year file, and our confirmation that it is on record. If the same component fails again on retest, the diagnosis was wrong or the parts were, and the plumber goes back; that is rare and we push to get it right the first time.

What it costs

Three numbers, all quoted before work:

• The repair. A rebuild kit and an hour or two of a plumber’s time for most DCVA and PVB failures; a relief valve rebuild for most RPZ failures. Replacement only for cracked bodies, obsolete devices, or the wrong device for the hazard.
• The retest. A second visit and a second $25 BSI report. Usually less than the original test when booked with the repair.
• Nothing for the notification. The 24-hour notice to the Region is part of the test.

The cost page covers how testing itself is priced.

Avoiding the next failure

A device that is about to fail usually shows it: an RPZ relief valve that spits when nothing is running, a PVB that sprays at start-up, a tester’s note that “check 1 is marginal.” When the test result is a pass with a comment, budget for a rebuild before next year rather than after. And keep the device where it can be reached and seen: not behind stock, not under a leak, not in a room nobody has a key to.