Why is the relief valve on my RP (Reduced Pressure) assembly discharging water?

If you’re seeing water discharging from the relief valve on your Reduced Pressure (RP or RPZ) backflow assembly, don’t panic—but don’t ignore it either.

An RP is designed to protect your drinking water by dumping water to atmosphere whenever it senses a hazardous condition. Sometimes a little discharge is a sign the device is doing its job; other times it signals wear, debris, or a plumbing issue you need to address.

Below, the Atlas Backflow Services team explains the most common causes, quick diagnostics you can do safely, and when to call for the Backflow Testing Orange County experts recommend.

Quick Answer

• A brief, occasional drip can be normal as pressures fluctuate.

• A steady stream or frequent cycling usually means a problem—often debris in the check valve, a failed relief valve diaphragm, or thermal expansion in your plumbing.

• Never cap or plug the relief port. It’s a safety vent by design.

When in doubt, schedule the Backflow Testing Orange County experts recommend with a certified tester like Atlas Backflow Services.

How an RP works—and why it dumps water

An RP (Reduced Pressure Principle Assembly) contains two check valves with a “reduced pressure zone” in between and a spring-loaded relief valve venting to atmosphere. Under normal conditions:

• Supply pressure passes the first check, drops across the zone, then passes the second check to your building.

• The relief valve stays closed because the zone pressure is adequately lower than supply and higher than atmospheric.

If the first check fouls, the differential pressure drops. To prevent backflow, the relief valve opens and discharges water. The same may happen during backpressure or backsiphonage.

In short, the relief valve is a safety mechanism, and water at the vent means the device is responding to conditions—or that internal parts need service.

Common reasons your RP relief valve is discharging

1. Debris on the first check valve

   • Sand, scale, or rust can prevent the check from sealing. This reduces the differential pressure across the zone, causing the relief to “weep” or run.

   • Especially common after municipal line work, new construction, or irrigation line repairs.

2. Worn or damaged internal components

   • Relief valve diaphragm/spring wear or pitted check valve seats cause leaks through the checks and frequent venting.

   • Rubber components age and harden; rebuilds are routine maintenance.

3. Thermal expansion in a closed plumbing system

   • If you have a water heater and a check/PRV that creates a “closed system,” heated water expands with nowhere to go. The RP sees the spike and vents.

   • A failed, undersized, or waterlogged thermal expansion tank is a top cause of intermittent discharge—often shortly after hot water usage or overnight.

4. Supply pressure spikes and water hammer

   • Rapid pressure fluctuations from the street main, irrigation valves snapping shut, or a failing pressure reducing valve (PRV) can momentarily force open the relief.

   • Chronic spikes often show up as frequent short bursts from the relief.

5. Incorrect installation or orientation

   • RPs must be installed level, at the right elevation, and with proper clearance and drainage. Incorrect support, twisted bodies, or flooded enclosures can impair operation and cause nuisance discharge.

6. Freezing or physical damage

   • Past freeze events can crack bodies and warp seats, leading to continuous leaking from the relief.

7. Downstream backpressure/back-siphonage events

   • Pumps, elevated piping, or system drains can temporarily reverse pressures and open the relief valve by design.

8. Testing ports or valves not fully closed

   • After a test, a slightly opened test cock or a not-fully-seated shutoff can mimic internal leakage.

If any of the above sounds familiar, it’s time for the Backflow Testing Orange County experts recommend to verify performance and pinpoint the cause.

How to quickly triage what you’re seeing

You can safely observe and note patterns before calling a pro:

• Pattern of discharge

  • Occasional drips during high-demand times = can be normal.

  • Steady stream or constant dripping = likely internal wear or debris.

  • Bursts after hot water usage or overnight = suspect thermal expansion/expansion tank issues.

• Isolate downstream to test

  • If you close the downstream shutoff (leaving the upstream open) and the relief valve stops discharging, the issue may be downstream-related (e.g., thermal expansion, backpressure).

  • If it continues to discharge with downstream closed, suspect first check leakage or relief valve wear.

• Check your thermal expansion tank

  • Located near the water heater. If it’s hot and heavy or waterlogged, it may have failed.

  • A properly sized, pressurized expansion tank is crucial in closed systems.

• Look for pressure problems

  • Faucets that surge, banging pipes, or a constantly humming PRV point to pressure spikes or a failing pressure regulator.

• Note recent activity

  • Irrigation start-up, city main flushing, or construction nearby often introduces debris.

Document what you see (timing, volume, whether it stops when downstream is closed) and share it with the technician from Atlas Backflow Services—it speeds diagnostics and reduces downtime.

What to do next

• Schedule certified testing and diagnosis

  • Annual certified testing is required by most Orange County water purveyors. It’s also the Backflow Testing Orange County experts recommend to catch small issues before they become emergencies.

  • Atlas Backflow Services performs full RPZ testing, differential checks, and provides a clear report for you and your water district.

• Professional cleaning or rebuild

  • If debris is the culprit, disassembly and cleaning of the checks and relief valve usually restores proper differential.

  • For worn parts, a rebuild kit (seats, springs, diaphragms) for brands like Wilkins/Zurn, Febco, Watts, Apollo, or Ames often resolves persistent discharge.

• Address system pressure and expansion

  • Verify PRV settings and performance; typical building pressure ranges from 50–75 PSI.

  • Install, right-size, or replace a thermal expansion tank if your system is closed.

  • Add water hammer arrestors where fast-closing valves (ice makers, irrigation, solenoids) cause spikes.

• Improve installation conditions

  • Ensure adequate drainage, correct orientation, and freeze protection.

  • For high-risk sites, consider an RPZ enclosure with a proper air gap and drain.

• Set up proactive maintenance

  • Have Atlas Backflow Services test before irrigation season and after any major plumbing changes—the Backflow Testing Orange County experts recommend this seasonal check for properties with complex systems.

FAQs

• Is it safe to cap the relief port to stop the leak?

  • No—never cap, plug, or route the relief discharge somewhere it can submerge. The relief port must discharge freely to atmosphere to protect your water supply and comply with code.

• Can I keep using water while it’s discharging?

  • Small, intermittent drips aren’t an emergency, but a steady stream means the device isn’t providing full protection or is experiencing abnormal conditions. Schedule service promptly.

• How long do RPs last?

  • The body can last decades, but rubber and spring components are wear items and often need service every 3–5 years depending on water quality and usage. Annual testing is the Backflow Testing Orange County experts recommend to verify ongoing protection.

Why choose Atlas Backflow Services

• Certified backflow specialists focused on RPZ, DCVA, PVB, and air gaps

• Fast diagnostics and repairs with OEM parts for leading brands

• Compliance handling with local Orange County water purveyors

• Transparent reporting and reminders so you never miss required testing

Whether your RP relief valve is dripping or dumping, Atlas Backflow Services will determine if it’s normal operation or a sign of wear, debris, or system pressure problems—and fix it right.Ready to stop the discharge and stay compliant?

Contact Atlas Backflow Services to book the Backflow Testing Orange County experts recommend and keep your water safe, your system efficient, and your property in compliance.