Quick Answer:
If the relief port stays open after test, first isolate the unit, relieve pressure, and inspect the internal spring and seat. Often the device won’t reseat because it is still pressurized, a spring is broken or corroded, or debris is trapped under the seat. Follow the steps below carefully; if any internal parts are damaged you’ll likely need a repair kit or a professional.
Why This Happens
- Residual pressure keeps the relief valve or test port from closing — the unit must be fully depressurized before the mechanism can reset.
- Broken, weak, or corroded springs fail to push the check or relief back to the closed position.
- Debris, mineral buildup, or a damaged seat prevents a proper seal and can leave the relief port open; this is related to issues like backflow preventer test port leaking.
- In rare cases, an internal failure can cause backflow behavior, similar to problems described for backflow preventer causing reverse flow, which requires immediate attention.
Step-by-Step What to Do
Step 1 — Close the isolation valves
- Shut the inlet and outlet isolation valves on the backflow assembly to stop supply and downstream flow.
- Confirm both are fully closed. This keeps water from pushing the relief open while you work.
Step 2 — Depressurize the unit
- Open a downstream faucet or bleed the test ports slowly to relieve pressure inside the device.
- Wait a minute and recheck pressure; use the test cocks to confirm no pressure is present before opening the housing or touching internals.
Step 3 — Inspect springs and seats
- With the unit depressurized and valves closed, remove the cover per manufacturer instructions and visually inspect springs, seals, and seats.
- Look for broken or corroded springs, mineral deposits, or tears in rubber seats. Light cleaning may remove debris; do not pry or force parts.
Step 4 — Try a controlled reset
- If springs and seats look intact, carefully manually reset the check or relief per the maker’s method—usually a gentle lift and release after depressurizing.
- Open the outlet isolation valve slowly to re-pressurize and watch the relief port. If it stays closed, restore service and monitor.
Step 5 — Repair or replace parts
- If springs are damaged or the seat is worn, replace the parts with the correct repair kit or replace the entire assembly if recommended.
- After any repair, repeat the isolation, depressurizing, and test sequence to ensure the relief port closes reliably.
What Not to Do
- Do not force reset lever — forcing can break internal parts or create a dangerous leak when pressure is restored.
- Do not work on the unit while it is pressurized; that risks sudden spray or injury.
- Do not use improvised parts or mismatched springs; incorrect parts can fail quickly and may violate local codes.
When to Call a Professional
- If the relief port still won’t close after you’ve isolated, depressurized, and inspected springs and seats.
- If you find corrosion, broken springs, damaged seats, or if the unit requires complex disassembly you’re not comfortable with.
- If the device is part of a critical system (irrigation with fertilizer, commercial plumbing, or municipal connections) where regulations require certified testing and repair.
Safety Notes
- Always shut isolation valves and fully depressurize before opening the backflow housing.
- Wear gloves and eye protection; mineral deposits or sudden drips can be sharp or dirty.
- Follow manufacturer instructions for disassembly and reassembly. If you’re unsure, stop and call a licensed plumber.
Common Homeowner Questions
- Q: How long should I wait after depressurizing before inspecting?
A: Wait a minute or two and verify pressure is zero at the test cocks. - Q: Can I temporarily tape the relief port closed?
A: No. Taping or blocking the port defeats the safety function and risks contamination or damage. - Q: Will a repair kit fix most problems?
A: Yes for springs and seats, but extensive corrosion or body damage usually means replacement.
For more related articles, see the Backflow Preventer Malfunctions hub.