RV Water Heater Pressure Relief Valve Leaking: Normal or Problem?

The Quick Answer

Steven, your 2025 Flagstaff Super Lite's Suburban water heater is experiencing thermal expansion pressure relief, which is causing the pressure relief valve to drip intermittently. The fact that it stopped dripping after you flushed the valve Saturday but resumed Monday morning, combined with your practice of keeping the electric element on continuously, strongly indicates this is a thermal expansion issue rather than a defective valve. Your dealer's advice to create an air pocket was on the right track, but the problem is that keeping the electric heater running constantly creates repeated heating cycles that build pressure in a closed system, eventually overwhelming even a proper air gap.

The root cause is that your RV's water system lacks a thermal expansion tank, which is common in many RVs. When water heats up, it expands by roughly 4-5% from cold to hot, and in a closed plumbing system with no place for this expanded water to go, pressure builds until the pressure relief valve opens at its rated pressure, typically 125 PSI. Since you've been running the electric element continuously since August, you're creating optimal conditions for this pressure buildup, especially if your incoming water pressure from the campground or your onboard pump runs on the higher side.

What's Causing This

The physics behind your water heater leak involves thermal expansion in a closed water system. Your Suburban water heater, like most RV units, operates as part of a closed-loop system when you're connected to city water or using your fresh water tank with the pump. When the electric heating element cycles on and off to maintain temperature, it heats the water inside the tank, causing it to expand. In a typical home water heater installation, thermal expansion tanks or other pressure relief mechanisms handle this expansion, but RV systems often rely on air pockets or the flexibility of the plumbing lines.

Your continuous operation of the electric element exacerbates this issue significantly. Most RV water heaters are designed for intermittent use, heating water as needed rather than maintaining constant temperature. By keeping it on all the time, you're creating frequent heating cycles, and each cycle builds pressure. The pressure relief valve on your Suburban unit is calibrated to open at 150 PSI to protect the tank from rupturing, which is exactly what it's doing when you see those drips.

The intermittent nature of your leak, where it stops after flushing but returns after a few days, indicates that the valve itself is functioning correctly but is responding to legitimate pressure buildup. When you flush the valve, you're temporarily relieving the pressure and clearing any debris that might prevent a complete seal, but as the heating cycles continue, pressure builds again until the valve must open to protect the system.

Another contributing factor could be your incoming water pressure. If you're connected to city water with pressure above 60 PSI, this higher baseline pressure means less thermal expansion is needed to reach the relief valve's opening point. Many campgrounds provide water at 80-100 PSI or higher, and when combined with thermal expansion, this quickly reaches the 150 PSI threshold where your pressure relief valve activates.

Tools You'll Need

For diagnosing and addressing this issue properly, you'll need several tools and materials. First, obtain a water pressure gauge with a hose connection thread, typically available at any hardware store for around $15-25. This will allow you to measure both your incoming water pressure and system pressure during heating cycles. You'll also need a basic multimeter if you plan to test electrical components, though this should only be done by qualified technicians following proper safety shutdown procedures, which costs about $20-30 for a decent digital unit.

Get yourself a water heater drain valve tool, which is a special socket designed to fit the drain plug on Suburban water heaters. This typically costs around $10-15 and will make draining and servicing much easier. You'll also need standard tools including adjustable wrenches, channel lock pliers, and a standard socket set. A garden hose and a bucket will be necessary for draining operations.

For materials, purchase pipe thread sealant or Teflon tape for any fittings you might need to remove and reinstall. Consider getting a water pressure regulator if you don't already have one, as this is crucial for preventing over-pressurization. A quality brass regulator runs about $25-40 and can be set to maintain safe pressure levels. You might also want to pick up a thermal expansion tank designed for RV use, though this is more of an advanced modification.

If you decide to replace the pressure relief valve as a precautionary measure, make sure to get the exact Suburban replacement part. The valve will have markings indicating its pressure rating and temperature rating, typically 125 PSI and 150°F for most Suburban units. Expect to pay around $25-35 for a genuine Suburban pressure relief valve.

Step-by-Step Fix

Begin by turning off both the electric and propane functions of your water heater, ensuring electrical power is disconnected and gas connections are secure, then allow it to cool completely, which takes several hours. Your safety is paramount when working with pressurized hot water systems. Once cooled, connect your water pressure gauge to a nearby faucet or water spigot to measure your baseline water pressure. If you're seeing readings above 60 PSI, this is contributing significantly to your problem, and installing or adjusting a pressure regulator should be your first step.

Next, properly drain your water heater system to create an adequate air pocket, but do this more thoroughly than your dealer likely described. Turn off your water pump or disconnect from city water, then open the hot water faucet closest to the water heater to break the vacuum. Remove the drain plug from the bottom of the Suburban unit using your drain valve tool, and allow the tank to drain completely. This process should take 10-15 minutes for complete drainage.

While the tank drains, inspect the pressure relief valve closely. Look for mineral buildup, corrosion, or debris around the valve seat. The valve should have a small lever that you can lift to test operation. When lifted, it should release water freely and snap back closed with a solid seal. If the valve doesn't operate smoothly or doesn't seal completely when released, replacement is necessary.

After complete drainage, reinstall the drain plug with fresh thread sealant, ensuring it's tight but not over-tightened, which could damage the tank threads. Now comes the critical part of creating a proper air pocket. Close your hot water faucet and begin refilling the system slowly. Fill the tank only about 80-85% full rather than completely full. You can monitor this by opening the pressure relief valve lever periodically during filling. When water flows steadily from the pressure relief valve, you've achieved full fill. At this point, drain out about 10-15% of the tank's capacity to create your air pocket.

The key behavioral change you need to make involves how you operate the electric heating element. Instead of running it continuously, switch to heating water only when needed. Turn on the electric element 30-45 minutes before you need hot water for showers or dishwashing, then turn it off afterward. This intermittent operation dramatically reduces the thermal expansion cycles that build pressure in your system.

Test your repair by turning the electric element on and monitoring system pressure with your gauge during a heating cycle. Normal operation should show minimal pressure increase if your air pocket is adequate and your incoming water pressure is regulated. If you still see pressure climbing toward the relief valve opening point, consult a qualified RV technician for further diagnosis.ef valve activation levels, you may need a larger air pocket or should consider installing a thermal expansion tank.

For the thermal expansion tank installation, mount a small RV-specific expansion tank in the hot water line near the water heater outlet. These tanks contain a rubber diaphragm that compresses as water expands, providing a buffer against pressure buildup. This is a more permanent solution that allows for normal water heater operation without the constant concern about thermal expansion pressure.

When to Call a Pro

While this repair is well within the capabilities of most DIY RV owners, certain situations warrant professional intervention. If you discover that your pressure relief valve is leaking from the threads or body rather than just the outlet, this indicates internal valve failure or tank corrosion that requires immediate professional attention. A water heater tank with corrosion issues can fail catastrophically, causing significant damage to your RV's interior.

Call a professional if your pressure testing reveals system pressures that remain high even after proper air pocket creation and pressure regulation. This could indicate internal tank problems, faulty heating elements, or thermostat malfunctions that create overheating conditions. Professional diagnosis can identify these issues before they lead to complete system failure.

You should also seek professional help if you're uncomfortable working with pressurized water systems or if your RV is still under warranty. Since your 2025 Flagstaff is quite new, warranty considerations are important. Document your repair attempts and consult with your dealer before making significant modifications like thermal expansion tank installation, as these changes could potentially affect warranty coverage.

Additionally, if you find yourself needing to repeat the air pocket creation process frequently, or if the problem persists despite following these procedures, there may be underlying issues with your RV's plumbing system design or installation that require professional evaluation. Some RV manufacturers use plumbing configurations that are more prone to thermal expansion problems, and experienced RV technicians can recommend system modifications to address these design limitations permanently.