Quick Answer:
If you see a continuous discharge from the relief port, the device is releasing water because an internal valve or pressure condition isn’t holding. Start by isolating the unit and checking for failed check valves, trapped debris, or improper pressure differential between inlet and outlet. These are the most common causes and the first things to inspect.
Why This Happens
- Check valve failure: If one of the check valves doesn’t seat, flow can push through the relief port to protect the system.
- Debris or corrosion: Particles or build-up can prevent valves from sealing tightly.
- Pressure issues: If the upstream and downstream pressures don’t stay within the correct difference, the relief port opens to discharge water.
- Worn relief mechanism: Springs and seals in the relief assembly wear over time and may stick or leak.
- Intermittent or related symptoms: If the device sometimes pulses or releases at odd times, see notes about releases water randomly and inspect for the same root causes.
Step-by-Step What to Do
1. Isolate the unit and observe
- Shut the upstream shutoff to stop main supply to the device if possible, then open a downstream tap to relieve pressure.
- Observe whether the discharge stops or slows when isolated. Continuous flow while isolated points to internal failure.
2. Inspect check valves
- Remove covers or caps per the manufacturer’s instructions to view check valve seats and discs.
- Look for misalignment, broken springs, or obvious damage. A stuck or failed check valve is a common cause of a constant relief discharge.
3. Clean debris
- Carefully remove small particles, sediment, or scale from seats and ports using a soft brush or cloth. Avoid sharp tools that can score sealing surfaces.
- Reassemble and test. Even small debris can prevent a proper seal and cause continuous dripping.
4. Verify pressure differential
- Measure inlet and outlet pressures with gauges or have a pro do this. The device needs a specific pressure differential to remain closed.
- If downstream pressure rises too high or upstream pressure drops, the relief port may discharge to protect downstream components.
5. Test the relief and test ports
- Follow the device’s test procedure. If the relief assembly or test port leaks even after cleaning and valve inspection, the relief mechanism or seals may need replacement.
- If you see a leak at a test port specifically, compare symptoms to those described for test port leaking to decide if repair or replacement is needed.
What Not to Do
- Do not cap discharge outlet — blocking the relief path can cause unsafe pressure and damage the unit or plumbing.
- Do not force or hammer internal parts; that can make seals worse or break components.
- Do not ignore a continuous discharge. Ongoing leaks can waste water and mask failing parts that could allow backflow.
- Do not replace parts without matching the manufacturer’s specifications; wrong parts can fail quickly.
When to Call a Professional
- If isolating and basic cleaning do not stop the discharge.
- If gauges show abnormal pressure differentials you cannot correct.
- If internal parts are broken, corroded, or the relief mechanism requires replacement — a licensed plumber experienced with backflow assemblies should handle repairs and retesting.
Safety Notes
- Turn off water and relieve pressure before removing covers or internal components.
- Use proper tools and follow the device manufacturer’s instructions. Keep small parts and springs organized during disassembly.
- If the device is part of a potable water system, ensure any replacements are certified for backflow assemblies and that the system is retested after repair.
Common Homeowner Questions
- Why is water coming out even when nothing is running? A failed check valve or pressure imbalance can force continuous discharge through the relief port.
- Can I just replace a seal myself? You can replace seals if you have the correct parts and follow instructions, but doubtful repairs or wrong parts can cause more problems.
- Will this fix stop automatic sprinklers from losing pressure? Fixing the relief discharge often restores correct pressure, but also check the sprinkler system for its own valves and leaks.
For more related articles, see the Backflow Preventer Malfunctions hub.