AO Smith Leaking From the Bottom
The Short Answer: Water at the base of an AO Smith ProMax, Signature, or State-badged twin is a drain valve, T&P discharge, a rotten nipple, an element gasket (electric), or the steel shell. Wipe, wait, name the wet part. A bead at the plastic drain is a valve. A wet jacket or water in the burner tray is a replacement — today. Generic map: leaking from the bottom.
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Search Intent & The Real Problem
You found a puddle. The badge says AO Smith. The internet said Flex Seal. I have replaced $12 drains on ProMax tanks that had years left, and I have cut out gas FVIR units someone “sealed” while the closet floor went soft. Gravity lies: T&P water, a connector, or a top-side anode weep runs to the pan and looks like a bottom leak. Hybrid Voltex condensate is a different drip — hybrid problems. This page is a tank AO Smith, water at the floor.
What other guides get wrong
They treat every AO Smith bottom drip as a cracked tank, then skip the paper-towel test. A plastic drain gets condemned. A T&P drip gets a new heater while house pressure is 110 psi. They ignore water on the burner — dripping on the burner / on the pilot. And they mix Voltex condensate with a tank-shell leak.
Step-by-Step Troubleshooting
Step 1: Name the wet part
| Wet location | Likely source | Next |
|---|---|---|
| Hose threads / cap of the drain | Valve not seated, grit on the seat | 3/4” brass, not more plastic |
| Pipe threads of the drain at the tank | Cross-thread or bushing weep | Stop if the bushing turns |
| T&P discharge pipe to the floor | Pressure or temperature | Gauge the house; never cap |
| Cold or hot nipple / dielectric / flex | Failed nipple or connector | Nipple or listed flex |
| Lower element (electric) | Gasket or stripped tank threads | Element + gasket if the shell is dry |
| Jacket, foam, rust streak at the base | Tank shell | Replacement |
| Gas: wet burner tray / rust ring | Tank into the combustion chamber | Shut gas. Replacement |
| Pan wet, tank dry | AC coil, T&P, or a fitting above | Keep looking |
- What to look for: Dry it. Wait two minutes. Wipe again. A drain-valve bead stays on the hose thread. A dead tank wets insulation in a patch that returns.
- Required tools: Paper towel, flashlight.
Sister brand, same gravity: Bradford White from the bottom.
Step 2: Kill energy and water the right way
- What to look for: Electric: double-pole off (4500 W / 240 V is ~18.8 A; confirm dead). Gas electronic control: knob to off / gas cock off. Cold inlet off. Hot faucet open so the tank can breathe.
- Required tools: Breaker lock or gas cock, hose, pan. No floor drain? This drain procedure.
You do not empty a 50-gallon to diagnose. Drop the level below the drain only if that valve is the repair.
Step 3: Drain valve, nipples, elements — the saves
- What to look for: Factory plastic 3/4” drain that cracked. Dielectric nipple weeping behind a flex — AO Smith hot-side nipples rot like everyone else’s. Lower-element gasket on a dual-element electric — ~12–13 Ω is a healthy 4500 W / 240 V element with power verified dead; a leak is the gasket, not the ohm reading. Related: gasket leak.
- Required tools: Two wrenches with a backup on the tank bushing, 3/4” brass ball drain, potable PTFE or dope.
If the tank bushing spins with the valve, stop. That is how you oval the opening and buy a heater. Do not gorilla a plastic valve “snug.”
Step 4: T&P water that ran to the pan
- What to look for: Static pressure over 80 psi at a hose bib. Waterlogged expansion tank (Schrader spits water) — expansion tank full. T&P that dribbles after someone lifted the test lever. Typical relief 150 psi / 210°F. Same physics as T&P after testing and overflow discharging.
- Required tools: Hose-bib gauge, tire gauge on the expansion tank.
Never plug the T&P. A stream is shut down and a licensed call. A brand-new AO Smith that weeps into the pan on first heat is often no expansion tank on a closed PRV system — new heater, water in pan.
Step 5: When it is actually the tank — especially gas FVIR
- What to look for: Water returning at the jacket with every fitting dry. Pinholes at the bottom head after the glass lining fails. Gas: water in the burner tray, rust at the combustion chamber, or a hiss into the FVIR screen. That vessel is scrap. Do not keep lighting it. Electric: foam wet around the lower element with the gasket dry is the shell, not another gasket.
- Required tools: None. Do not epoxy, Flex Seal, or “tank repair kit” a pressure vessel.
A 12-year ProMax in hard water with a virgin anode was on borrowed time. The leak is the funeral, not the disease.
When DIY Ends: Calling a Licensed Pro
Stop if the closet is flooded near 240 volts, the bushing spins, the jacket is wet, you smell gas, water is in the burner tray, or the T&P is streaming. A plastic drain on an otherwise dry tank is a homeowner job if you can isolate it. A leaking shell is a permitted replacement in many cities. Same-day licensed swap beats a collapsed subfloor.
Frequently Asked Questions
Q: Why is my AO Smith leaking from the bottom? A: Drain valve, T&P discharge that ran down, a nipple or element gasket, or the steel shell. Wipe each part. A bead at the drain is not a dead tank. A wet jacket or a wet burner tray is.
Q: Can I repair an AO Smith leaking from the bottom? A: You can replace a drain valve, a nipple, or an element gasket. You cannot repair a hole in the tank. Water in the combustion chamber is shut-gas and replace.
Q: Should I shut the AO Smith off if it is leaking from the bottom? A: Yes if it is more than a slow valve weep you are about to replace, and always if the jacket is wet, the pan is filling, or the burner tray is wet. Close the cold inlet, kill power or gas, keep the T&P open to atmosphere.