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By the time you find water from a plumbing leak inside your RV, damage may already be done. A pressure test lets you check for leaks before you fill the lines with water.
Once you have the equipment, the test is free to do yourself, takes about 15 minutes, and could save you thousands in water-damage repairs.
Here’s exactly what you need and how to perform the test.
What an RV Plumbing Pressure Test Can Tell You
A plumbing pressure test uses air and a gauge to check for leaks in your RV’s freshwater lines. A tester connects to the city-water inlet, the plumbing is pressurized, and the air source is disconnected. Then you watch for a pressure drop.
You can see the process in action in the video below.
What it can do:
- Flag a possible plumbing leak. Falling pressure gives you a reason to investigate, even if you haven’t seen any water.
- Check lines you can’t easily inspect. A leaking connection behind a cabinet or beneath the floor can affect the gauge reading.
- Test drained plumbing before you refill it. You can look for a problem before introducing water that could escape through a damaged connection.
What it can’t do:
- Tell you exactly where the leak is. You still have to track down the source, starting with the tester’s own connections.
- Check components excluded from the test. A bypassed water heater, for example, needs a separate check.
Can’t You Just Listen for the Water Pump?
You can, but you have to fill the lines with water first. If a fitting behind a cabinet is leaking, water is escaping while you wait to hear the pump kick on. An air test lets you check drained plumbing before filling it with water. That’s a good reason to do it before de-winterizing.
For an RV you’re already using, the pump can help you spot a problem. With city water disconnected, let the pump pressurize the lines, then shut it off. Once air has cleared from the plumbing and every fixture is closed, it should stay off. If it starts again without anyone using water, check for leaks. Water could also be leaking backward through the pump into the freshwater tank.
The catch is that the pump only restarts after pressure falls to a certain point. A small leak may take longer to trigger than you have time to listen. A suitable gauge lets you see pressure changes without waiting for the pump to start.
How to Pressure-Test Your RV’s Water Lines
You’ll need a pressure-test kit and a clean, oil-free air source, such as a suitable tire inflator. Look for a tester with a gauge and an adapter that holds the city-water inlet’s check valve open. Otherwise, that valve can keep the gauge from showing small pressure losses inside the RV.
An ordinary winterizing blowout plug won’t do this. RecPro sells an adapter made for this test, but that listing is for the fitting alone. You would still need the gauge and air connections, which you can get as a kit on the RVTI website.
Use 80 PSI of air pressure for this test, the lower end of the range specified in RVIA’s factory testing procedure. Before adding air, bypass the water heater and any pressurized water-storage tank, and isolate any connected equipment that cannot be air-tested at 80 PSI. Once you reach the test pressure, disconnect the air source, leave the gauge attached and watch for pressure loss for at least 10 minutes
Tools Needed:
- RVTI Water Test Kit: Includes the pressure gauge, brass fittings, and city-water adapter. The kit requires assembly, and this listing offers shipping.
- AstroAI Cordless Tire Inflator: Supplies air for the test. You can also use a suitable inflator you already own.
- Needle-nose pliers: For gently pulling out the inlet’s screen washer if your adapter requires its removal.
Have wrenches and suitable thread-seal tape ready to assemble the tester per the instructions. The RVTI kit already includes the adapter, so you won’t need to purchase the RecPro fitting separately.
1. Get the plumbing ready
Start with drained water lines, the city-water hose disconnected, and the water pump and water heater switched off. Let the heater cool before doing any draining.
For a test with the water heater bypassed, set its bypass valves accordingly. Check the instructions for filters, tankless heaters, and other connected appliances, too. Their setup can differ from the tank-style heater shown in the video.
2. Close the faucets and drains
Check both handles on every faucet, including the inside and outside showers. Close the low-point drains after draining the lines.
At the shower, close the faucet handles rather than relying on the pause button on the showerhead.
3. Connect the tester
Follow the adapter’s instructions about removing the inlet screen or washer. The fitting in the video has its own gasket, so the existing screen washer comes out first.
Screw the tester into the city-water inlet and check that its connections are snug.
4. Add air slowly
Watch the gauge as you bring the plumbing up to the approved test pressure. Stop adding air, then disconnect the inflator or close the tester’s air-supply valve.
Leave the gauge connected to the RV. Keeping an air source feeding the lines could replace escaping air and hide a leak.
5. Watch the reading
Allow the pressure to settle, then note the reading and start your timer. The test shown in the video runs for about 10 minutes; RVIA’s published manufacturing procedure also specifies a minimum 10-minute hold. Follow any longer period required for your RV’s test.
If pressure keeps falling, check the tester’s connections before looking for a leak inside the RV. A steady reading shows no detectable pressure loss during that test.
6. Release the pressure
Slowly open a faucet and wait for the gauge to reach zero before removing the tester. Reinstall the inlet screen and washer if you removed them.
The Pressure Dropped. How Do You Find the Leak?
Check the test equipment first
In Rigor RV Inspection’s video, the pressure initially drops fast enough to suggest a plumbing leak. After he tightens the tester’s connection at the city-water inlet, that loss slows. A poor seal at the tester can send you looking for a problem inside the RV.
With the system pressurized, check the adapter connection, gauge fittings and air-fill valve with soapy water or a leak-detection liquid safe for those materials. Brush or spray it onto the outside of each connection and watch for bubbles that keep growing. Small leaks may take a minute or longer to show up. Wipe away the solution afterward.
Before loosening any fitting, release the air through a faucet and wait for the gauge to reach zero. Inspect the adapter’s washer for damage or poor seating, reconnect it, and repeat the test.
Recheck faucets, drains, and valves
Go back through the RV and check every faucet, including the outside shower. Shut the shower off at its controls, rather than relying on the pause button on the showerhead.
Check the low-point drains, toilet water valve, and any handheld sprayers. Confirm the water-heater bypass valves are fully in their intended positions. On an RV with a city-water/tank-fill selector, check that it’s set to city water.
An open drain or a faucet left slightly on lets air out without a broken pipe or fitting.
Work through the plumbing you can reach
Start under the sinks, around the toilet’s water connection, and in the compartments with the pump and water-heater bypass plumbing. Use a flashlight and existing service panels to follow the lines as far as you can.
Apply the same bubble test to accessible joints, elbows, tees, and valve connections. Include any filter housing that remains connected during the test. Keep the liquid away from electrical components.
Turn off nearby fans and listen for escaping air, too. A hiss can help you narrow the search, but a small leak may be too quiet to hear. Keep the pressure at the test setting instead of increasing it to make the leak louder.
Mark any leaking connection you find. Release the pressure before attempting a repair, then test again. Finding one leak doesn’t rule out another.
Consider leakage back through the pump
Pressure can also escape backward through the water pump toward the freshwater tank. Rigor RV Inspection points out this possibility in his video.
The pump’s check valve should prevent reverse flow. If it fails to seal, water supplied through the city-water connection can pass backward into the freshwater tank.
During an air test, that path can let pressure escape without producing bubbles at an exposed plumbing connection. If you’ve previously noticed your freshwater tank filling while using city water, mention that when having the pump checked. A falling gauge alone won’t identify the pump as the cause.
Get help when the leak is out of reach
If the tester seals properly, the valves are closed, and the accessible connections check out, the remaining plumbing may need to be tested in sections. A technician can isolate the pump and individual branches to narrow down where pressure is escaping.
You don’t need to start pulling off wall panels or cutting into the enclosed underbelly based only on a falling gauge. Tell the technician your starting pressure, how much it dropped, how long that took, and which connections you checked.
After repairs, repeat the pressure test before filling the lines with water.
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