RV Water Heater Leak: How to Find the Source Safely

An RV water heater leak almost always comes from one of five spots: the pressure relief (T&P) valve, the drain plug or anode rod, the tank’s inlet/outlet fittings, the bypass valve, or a cracked tank shell from freeze damage. Finding the exact source before you touch anything matters, because a cracked tank means replacement, while a loose fitting is a five-minute fix. Here is how to isolate the source safely.

Shut everything down first

Before inspecting, turn off the water pump (or disconnect city water), switch off the propane and 120V electric heating elements at the water heater’s control panel, and let the unit cool if it was recently running. Working on a pressurized, hot tank risks scalding and makes small leaks harder to see under residual pressure. Open a hot water faucet inside the RV briefly to relieve pressure in the lines.

Check the pressure relief (T&P) valve first

This is the single most common leak point on both Suburban and Atwood/Dometic units. It is a brass valve with a lever, mounted on the tank, with a small drain tube running to the outside. A slow drip here is often just mineral debris holding the valve seat open slightly, or a valve reaching the end of its service life (they are rated for a few years and are inexpensive to replace). Lift the lever briefly to flush debris, then watch if dripping stops; if it continues, replace the valve rather than trying to reseat it.

Check the drain plug and anode rod

Suburban water heaters use a sacrificial anode rod that doubles as the drain plug; Atwood/Dometic units typically use a plastic drain plug (sometimes called a “Gemini” style plug) without an anode, since their tanks are aluminum. Leaks here usually mean the plug’s seal (a nylon washer or the anode’s threads) is worn, cross-threaded, or simply needs fresh Teflon tape or a new gasket. An anode rod eaten down to a thin wire also loses its ability to seal properly and should be replaced anyway as part of normal maintenance.

Check the bypass valve and fittings

The bypass valve, used to route water around the tank during winterizing, has multiple valve seats that can develop slow seepage over time, especially if it was left mid-position. Inlet and outlet fittings where the water lines connect to the tank can also loosen from vibration during travel. These are usually fixable by hand-tightening or replacing a worn O-ring, without needing to touch the tank itself.

When it is the tank itself

If water is coming from the tank’s outer shell rather than a fitting, the most common cause is freeze damage: water left in the tank expanded and cracked it during a hard freeze while not winterized, or the bypass valve was not properly switched before adding RV antifreeze. A cracked steel or aluminum tank cannot be patched safely and needs to be replaced as a unit, which is why confirming the exact source before assuming a simple part fix matters.

Frequently Asked Questions

Can I keep using my RV water heater while it has a small leak?

Only if the leak is clearly from an external fitting and not the tank body, and even then it is safer to fix it promptly, since ongoing moisture near the unit’s electrical or gas components can create a bigger hazard than the original leak.

Why does my RV water heater leak only when the engine is running or while driving?

This points to a loose fitting or a valve vibrating open slightly during travel, rather than a tank crack, since a cracked tank would typically leak regardless of whether the vehicle is moving.

How often should the anode rod be checked?

Most manufacturers recommend checking it at least once a year, or every few months for RVs used heavily or stored near saltwater, since a badly corroded anode both fails to protect the tank and loses its ability to seal the drain opening.