Seeing water dripping out of your rv hot water heater pressure relief valve can be a bit of a heart-sink moment when you're out at a campsite. You're just trying to enjoy a morning coffee, and suddenly you notice a small puddle forming right underneath that exterior access panel. The good news is that a weeping valve isn't always a sign of a total disaster. In fact, more often than not, it's just the valve doing exactly what it was designed to do—or it's a sign that your water heater has lost its "breath."
What's the Point of This Valve Anyway?
Before we start tearing things apart, it's worth knowing why that little brass lever is there in the first place. This component is often called a P&T valve, which stands for pressure and temperature. Its job is pretty straightforward: it's a safety device. If the water inside your tank gets too hot or the pressure climbs too high, this valve pops open to let some of that energy out. Without it, your water heater could, in extreme cases, turn into a literal rocket.
Because RV water heaters are smaller and undergo a lot of vibration from travel, they can be a bit more temperamental than the one sitting in your basement at home. The valve is usually set to open if the temperature hits about 210 degrees Fahrenheit or if the pressure exceeds 150 PSI. If you see it dripping, it's usually because one of those thresholds is being nudged, or there's a mechanical reason it can't seal properly.
Why is My Valve Leaking?
If you notice a steady drip, don't run out and buy a new one just yet. There are a few common reasons why an rv hot water heater pressure relief valve might start acting up, and most of them don't involve replacing parts.
The Missing Air Pocket
This is the most common culprit. When your RV water heater is manufactured, it's designed to have a small pocket of air at the very top of the tank. Since water expands when it's heated, that air pocket acts like a shock absorber. It compresses as the water expands, keeping the pressure at a manageable level. Over time, that air can get absorbed into the water, leaving no room for expansion. When that happens, the expanding water has nowhere to go but out through the relief valve.
Mineral and Scale Buildup
If you've been camping in areas with hard water, calcium and other minerals can build up right on the seat of the valve. Even a tiny speck of grit can prevent the valve from closing all the way. If it can't make a watertight seal, it's going to drip constantly, no matter how much you jiggle the handle.
Thermal Expansion from the Campground Source
Sometimes the problem isn't your heater at all; it's the campsite's water hookup. If the campground has very high water pressure and you aren't using a pressure regulator on your hose, your system is already under stress before you even turn the heater on. Once the water starts heating up, it pushes the pressure over the limit almost immediately.
Restoring the Air Pocket
If you suspect your tank has lost its air cushion, there's a simple way to get it back without any tools. You'll want to do this when the water is relatively cool so you don't scald yourself.
First, turn off your water heater (both the gas and electric switches) and turn off your water pump or the city water connection. Open a faucet inside the RV to let some of the pressure out. Now, go outside to the heater panel and pull the handle on the rv hot water heater pressure relief valve so it stays open. You'll hear some water glug out.
Next, open the bottom drain plug on the tank and let about a gallon or two of water out. Once you've done that, close the drain plug and snap the relief valve shut. When you turn your water back on, don't open the relief valve. Just turn on a hot water faucet inside to bleed the air out of the lines. This process leaves that necessary bubble of air trapped at the top of the tank, which should stop the weeping.
How to Clean a Gritty Valve
If restoring the air pocket didn't work, you might have some "gunk" in the valve. Sometimes you can clear this by "burping" the valve. With the water pressure on and the heater hot, quickly flip the silver lever up and let it snap back down. The rush of water can sometimes wash away any sediment that was stuck on the seal.
A word of caution: Be extremely careful when doing this. The water coming out is boiling hot and can spray in unpredictable directions. Stand to the side and maybe use a long screwdriver to flick the lever if you want to keep your hands clear.
If burping it doesn't work, you can try a vinegar soak. Some RVers will pump a few gallons of white vinegar into their water system and let it sit in the heater tank for a day. This helps dissolve the calcium buildup not just on the valve, but on the heating element too. It's a great piece of annual maintenance that keeps the whole system running longer.
When It's Time to Replace the Valve
Sometimes, the internal spring just gets weak, or the seal is too damaged to save. If you've tried the air pocket trick and you've flushed the tank, but it's still dripping, it's time for a replacement. Thankfully, these parts are standard and relatively cheap. You can find them at any RV supply store or even most hardware stores.
Getting the Right Part
Most RV hot water heaters (like those from Suburban or Atwood/Dometic) use a 3/4-inch NPT valve. However, you should always check the tag on your current valve to be sure. It will list the pressure and temperature ratings. Most are rated for 150 PSI and 210°F. Make sure the "probe"—the long metal rod that sticks into the tank—is the same length as your old one.
Steps for Replacement
- Cool Down: Turn off the heater and let it sit for a few hours. You do not want to work on a hot tank.
- Drain: Turn off your water supply and drain the tank completely using the drain plug at the bottom.
- Remove: Use a wrench (a deep socket or a crescent wrench works best) to unscrew the old rv hot water heater pressure relief valve. It might be a bit stubborn if it's been there for years.
- Prep: Clean the threads on the tank opening. Wrap the threads of your new valve with Teflon tape (plumber's tape) or use a bit of pipe dope to ensure a leak-proof seal.
- Install: Screw the new valve in by hand first to make sure you don't cross-thread it, then tighten it with your wrench until the lever is facing a convenient direction (usually down or out).
- Test: Refill the tank, turn the water on, and check for leaks before you turn the heat back on.
Don't Just Plug It!
This is the most important thing to remember: Never, under any circumstances, should you just screw a plug into the hole where the rv hot water heater pressure relief valve goes. I've seen people do this when they're frustrated by a leak and just want to finish their trip.
Plugging that hole turns your water heater into a potential bomb. If the thermostat fails and the heater stays on, the pressure will build until the steel tank literally rips apart. It's a safety feature for a reason. If it's leaking, fix it or replace it, but never bypass it.
Final Thoughts on Maintenance
A little bit of attention goes a long way with RV plumbing. Every time you de-winterize your rig, take a second to look at the valve. Check for any crusty white buildup around the edges. If you're proactive about flushing your tank once a year to get rid of the "white flakes" (calcium deposits), your rv hot water heater pressure relief valve will likely last as long as the RV itself.
It's one of those small parts that you don't think about until it starts making a mess, but once you understand how it works, it's a pretty easy fix. Stay dry, keep your air pocket intact, and enjoy those hot showers on the road!