RV Water Heater Leaking Outside
The Short Answer: Water on the ground under an RV heater door is a drain plug, T&P tube, anode, element gasket, or the steel (or aluminum) shell. It is not automatically a new 6-gallon. Wipe the wet part on the tank, not the dirt. A bead at the plug is a gasket. A wet jacket with rust at the seam is a replacement — today, not after a smear of silicone.
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Search Intent & The Real Problem
You hooked to city water or ran the pump and found a dark spot under the exterior water-heater door. Residential tanks hide in a pan. Yours dumps onto the frame and the campsite. Forums condemn the tank on every drip. I have replaced $4 drain-plug washers on Suburbans that had years left, and I have cut out tanks someone “sealed” while the bay floor went to mush and the DSI board sat in a puddle.
Gravity still lies. A T&P that is relieving through the factory tube looks like a bottom leak. A bypass valve weeping inside the cabinet tracks along the floor and out the door. Tankless boxes in the same hole — Girard, Suburban Nautilus, Truma AquaGo — leak from an exchanger or a relief, not a 6-gallon plug. Name the wet fitting before you buy a heater. House-tank map if this is a stick-built closet: leaking from the bottom.
What other guides get wrong
They treat every drip under the door as a cracked tank and then recommend RV silicone on the shell. A glass-lined steel Suburban that has a hole is scrap. An Atwood/Dometic aluminum tank with a pinhole is also scrap. They skip the paper-towel test, so a crushed drain-plug washer gets a $900 heater, or a T&P drip gets a new tank while city water is 95 psi with no regulator. They mix Suburban plugs with Atwood combination anode-drains and order the wrong part.
Step-by-Step Troubleshooting
Step 1: Name the wet part on the tank — not the dirt
| Wet location | Likely source | Next |
|---|---|---|
| Hose-thread / hex drain plug at the bottom of the tank | Missing or crushed washer, sediment on the seat, cross-thread | New washer or listed plug. Stop if the tank boss turns |
| T&P body or the little discharge tube aimed at the ground | Pressure or temperature — not the tank | Gauge city water; never cap |
| Anode hex (Suburban steel tanks, often separate from the drain) | Weeping plug or wasted rod | Anode + gasket, not a “bottom leak” |
| Electric element flange behind the interior or exterior cover | Gasket or stripped tank threads | Element + gasket if the shell is dry — gasket leak |
| Inlet/outlet or bypass valves inside the coach | Fitting, PEX crimp, winterize valve | Dry the bay; the water ran out the door |
| Jacket, foam, rust streak, water returning with fittings dry | Tank shell | Replacement |
| Burner tray / combustion chamber wet, rust ring | Tank into fire | LP off. Do not fire it |
| On-demand box, no 6-gallon tank | Exchanger, relief, filter housing | Brand tankless page, not a drain plug |
| Sight window wet from inside the door | Combustion leak or spray, not always the tank — sight glass | LP off |
- What to look for: Dry it. Wait two minutes. Wipe again. A drain-plug bead stays on the washer. A dead tank wets insulation in a patch that returns. Water only while city water is connected, dry on the pump, is often T&P or a city-inlet check — pressure, not a hole.
- Required tools: Paper towel, flashlight, a photo of the door badge (Suburban SW6DE / SW10DE vs Atwood/Dometic vs Girard/Truma).
Step 2: Kill energy and water the right way
- What to look for: Interior electric and gas switches off. Shore cord unplugged or pedestal breaker off. LP bottles closed if you are going near the burner. City-water connection off, pump off. Open a hot faucet so the tank can breathe. Six gallons is not a 50-gallon — it drains fast and it dry-fires fast.
- Required tools: Bottle wrench, the interior switches, a pan under the door. Do not hit Suburban reset on a tank you just emptied.
You do not dump the whole tank to diagnose a plug weep. You drop the level below the plug only if that plug is the repair.
Step 3: Drain plug, anode, element — the saves
- What to look for: Suburban: 1/2-inch NPT drain at the bottom of the tank, rubber washer that flattens or splits after winterize. Atwood/Dometic: many GC/GE tanks use a combination anode drain — that plug is the anode. When the rod is gone, the threads weep and then the shell goes. A plastic plug someone installed “because brass seizes” cracks on the highway. Element flange on dual-fuel units (~1400–1440 W at 120 V; a healthy element is near 10 Ω with power verified dead — not the 12–13 Ω of a 4500 W / 240 V house tank).
- Required tools: Correct wrench with a backup on the tank boss, new listed washer or OEM plug/anode, potable PTFE. Meter only with shore power locked off.
If the tank boss spins with the plug, stop. That is how you oval the opening and buy a heater in a campground parking lot. Do not gorilla a plastic plug “snug.” Do not epoxy the boss.
Step 4: T&P water that ran out the door
- What to look for: City-water hose connected, no regulator, or a regulator that died. Static over ~80 psi at a hose bib will lift a healthy RV relief (typical 150 psi / 210°F — confirm the stamping). Heat plus a check valve at the city inlet is a closed system: six gallons has nowhere to expand, so the T&P becomes the expansion tank and drips on the gravel. Same physics as a new residential T&P. A stream, not a bead, is shutdown — stuck open.
- Required tools: Hose-bib / city-inlet gauge. A 40–50 psi RV regulator that actually works.
Never cap, plug, or crimp that valve to “stop the leak outside.” You just built a bomb in a 6-gallon box. A T&P that dribbles after someone lifted the test lever may not reseat — replace the valve, do not keep cycling it.
Step 5: When it is actually the tank — or the exchanger
- What to look for: Water returning at the jacket with every fitting dry. Rusty water at a hot tap, popping for years, anode never changed, Suburban steel 8–12+ years of hard campground water. Pinholes at the bottom head. Water in the burner tray or a rust ring at the combustion chamber — that tank is done, and it is a carbon monoxide problem if you keep firing it. Same rule as water on a gas burner. Tankless: a wet exchanger is replacement, not JB Weld.
- Required tools: None on a wet shell. Do not silicone, Flex Seal, or “tank repair kit” a pressure vessel.
Electric still “works” on a weeping tank is not a save. 120 volts in a wet thermostat bucket is how you cook the ECO and the harness. Gas-side diagnosis on a dry tank is a different page: Suburban not working on gas, Atwood troubleshooting.
When DIY Ends: Calling a Licensed Pro
Stop if the bay is flooded near 120 volts, the tank boss spins, the jacket is wet, you smell propane, the T&P is streaming, or water is in the burner. A drain-plug washer on an otherwise dry Suburban is a homeowner job if you can isolate and drop the level. A leaking shell is a replacement — many campgrounds will not let you keep dumping gray-looking tank water under the rig. Same-day mobile RV tech beats a rotten bay floor and a DSI board sitting in a puddle. Do not keep rolling with a wet-vac and hoping.
Frequently Asked Questions
Q: Why is my RV water heater leaking outside? A: Drain plug washer, T&P discharge that ran to the ground, an anode plug, an element gasket, a bypass fitting inside that tracked out, or the tank shell. Wipe each part. A bead at the plug is not a dead tank. A wet jacket is.
Q: Can I fix an RV water heater that is leaking under the door? A: You can replace a drain-plug washer, an anode, a T&P, or an element gasket. You cannot repair a hole in the tank or a cracked tankless exchanger. Silicone on the shell is a delay until the bay floor fails.
Q: Should I shut the RV water heater off if it is leaking outside? A: Yes if it is more than a slow plug weep you are about to reseat, and always if the jacket is wet or the burner tray has water. Close city water and the pump, kill electric and LP, and keep the T&P open to atmosphere.