RV Water Heater Leaking From the Bottom
The Short Answer: Water at the bottom of an RV water heater is a drain plug, a P&T discharge, an anode (Suburban steel), a bypass fitting, or the tank shell. It is not automatically a new 6-gallon. Wipe, wait, name the wet part. A bead at the plug is a washer. A wet jacket or water in the burner box is a replacement — today. Residential map: bottom of the tank.
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Search Intent & The Real Problem
You opened the exterior door and the bay is wet. Forums sold Flex Seal and “they all weep.” Gravity lies in a coach the same way it lies in a closet: P&T water, a loose drain plug, and a bypass valve all run to the same corner. Suburban SW6DE / SW10DE steel tanks have a drain and often an anode. Atwood/Dometic aluminum tanks usually have a drain plug and a P&T — not a residential plastic hose bib. Girard and Truma tankless drips are a different box — Girard, Truma. This page is a tank RV heater, water at the floor of the bay.
What other guides get wrong
They treat every drip as a rotten tank, or they treat every tank as a Suburban anode. Atwood/Dometic aluminum often has no sacrificial anode to “replace as the leak.” They skip the paper-towel test, so a P&T drip on city water at 90 psi gets a new heater. They tell you to snug a drain plug with a cheater until the spud spins. And they mix residential 3/4” plastic drains with the square-head plug on a 6-gallon.
Step-by-Step Troubleshooting
Step 1: Name the wet part — door open, paper towel
| Wet location | Likely source | Next |
|---|---|---|
| Square-head / hex drain plug at the bottom | Washer, under-tight, or over-tight cracked tank | New fiber washer, snug, not gorilla |
| Anode hex (Suburban steel, some models) | Weeping threads or a rotten rod | Anode + seal, not “the tank” yet |
| P&T valve body or its discharge | Pressure or a dirty seat | Gauge city water; never cap |
| Bypass valves / winterize tees behind the heater | Valve stem or a cracked PEX | Valves, not a tank |
| Cold/hot fittings at the back | Back-side plumbing | Access from inside |
| Jacket, foam, rust streak, or water in the burner tray | Tank shell | Replacement |
| Bay wet, heater dry | AC drain, fridge, or a roof leak | Keep looking |
- What to look for: Dry it. Wait two minutes. Wipe again. A plug bead stays on the threads. A dead tank wets insulation in a patch that returns. Identify Suburban vs Atwood/Dometic on the door badge, not the coach decal — Suburban gas, Atwood troubleshooting.
- Required tools: Paper towel, flashlight.
Step 2: Kill water and energy the right way
- What to look for: City hose disconnected or its valve off. Pump off. Electric switch off; unplug shore or kill the pedestal before the cover. LP bottles off if you are in the burner box. Open a hot faucet so the tank can breathe. You do not dump 6–10 gallons on the campsite pad to diagnose a plug drip.
- Required tools: Hose disconnect, the interior switches.
If the tank is already empty, do not hit electric — Suburban reset only on a full tank.
Step 3: Drain plug, anode, and fittings — the saves
- What to look for: Factory plug with a missing or shredded washer. Suburban anode that has never been touched in eight years of hard campground water. Dope or PTFE on threads, not on the washer face if the design seals on the fiber ring. Backup wrench on the tank spud. If the spud turns with the plug, stop. That is a new heater. Bypass valves in the cabinet that were left half-open for winterize and now weep.
- Required tools: Correct socket for that plug, spare washer, two wrenches. No chisel.
Do not epoxy the shell. Do not overtighten a plug into aluminum.
Step 4: P&T water that ran to the bay floor
- What to look for: City-water pressure over ~80 psi with no regulator on the hose — the 6-gallon becomes the expansion tank. Overfilled tank, then a heat cycle: the P&T (often 150 psi / 210 °F, confirm the stamping) dribbles. Lever someone lifted to “test” and the seat never reseated. Hard stream: shut city and pump. Never cap. Full P&T drip path: RV pressure relief dripping.
- Required tools: Hose-end regulator, a gauge at the city inlet.
The bay floor is a witness, not a diagnosis.
Step 5: When it is actually the tank
- What to look for: Water returning at the jacket with every fitting dry. White crust on aluminum Atwood/Dometic, rust on Suburban steel, a rust ring in the burner pan. Water in the combustion chamber: shut LP. That tank is scrap. Pinholes after bypassing with RV antifreeze left in for a season, or after dry-camp electrolysis. Age 10+ years of campground water is a replacement conversation, not a kit.
- Required tools: None. Do not Flex Seal a pressure vessel on a rolling chassis.
When DIY Ends: Calling a Licensed Pro
A weeping drain washer is a campsite job if you can isolate water and you do not spin the spud. Stop if the jacket is wet, the burner tray has water, the P&T is streaming, you smell propane, or the plug bung is turning. A licensed RV tech or a mobile plumber beats a rotten floor and a CO bay. Same-day swap on a 6-gallon is cheaper than a slide-out soaked from below.
Frequently Asked Questions
Q: Why is my RV water heater leaking from the bottom? A: Drain plug, P&T discharge, anode threads, a bypass fitting, 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 from the bottom? A: You can replace a drain washer, an anode, or a P&T. You cannot repair a hole in the tank. Sealant on the shell is a delay until the bay floor fails.
Q: Should I use the RV water heater if it is leaking from the bottom? A: Not if the jacket is wet or water is in the burner box. Shut city, pump, 120 V, and LP. A slow plug weep you are about to reseal is the exception — still kill electric until it holds water.