THE SHORT VERSION
- Most water near a heater is not a failed tank. A.O. Smith’s manual says “many suspected ‘leakers’ are not leaking tanks”: fittings, valves, condensation and nearby appliances come first.
- Find the highest wet spot. Wipe everything dry, then check pipe joints and threaded fittings with a paper towel or cotton swab. The leak is at or above the first wet point.
- Usually fixable: pipe connections, the relief valve and its threads, the anode and drain valve fittings, electric element gaskets, and condensate lines on tankless and heat pump models.
- Usually a replacement: water from the tank body, a seam or a welded fitting with every connection dry. Leaking tanks can’t be repaired.
- Gas tanks can drip without leaking. Combustion condensation is common on a new or cold tank and should stop within about 1–2 hours of the water heating up.
Dry it, then find the highest wet spot
Water runs down pipes and the outside of the tank and collects at the lowest point, so the puddle tells you little. A drip at a joint on top can run inside the jacket and show up at the base. Find where water first appears, then match it to the table below.
Make it safe if the water is heavy
If water is spraying or pouring, shut the cold-water valve above the heater and turn off the gas or the breaker. See water heater emergency. For a slow drip, carry on.
Wipe everything dry
Floor, drain pan, tank top, pipes and relief valve. Note the time.
Test each fitting
Press a dry paper towel on every joint on top, the relief valve and its pipe opening, and the drain valve. Where a threaded fitting enters the tank, A.O. Smith’s manual says to slide a cotton swab between the jacket and the fitting: a wet swab means that fitting leaks. Mind hot pipes.
Note when it happens
After showers? Only while the burner runs? Only on a new heater? Timing separates condensation and pressure relief from a steady leak.
Look again in a few hours
The first spot that is wet again is the leak, or where water from above reaches the tank.
Where the water appears and what it usually means
| Where it’s wet | Usual cause | How to confirm | Verdict |
|---|---|---|---|
| Pipe joints on top | Loose or corroded connection, or a sweating cold pipe in humid weather | Paper towel on each joint; check whether the pipe is wet all along | Repair (tighten or replace the connector) |
| Where a fitting enters the tank top | Thread seal failing at the hot, cold, anode or relief valve fitting | Cotton swab between jacket and fitting comes out wet | Repair (drain and reseal) |
| Draft hood or vent (gas) | Flue gas condensing in a vent that isn’t working right | Water drips from the hood or vent pipe, often while the burner runs | Call a pro or the gas utility; not a tank leak |
| End of the relief valve pipe | Valve opening on pressure or temperature | Drips during or after heating, or a burst of hot water | Find the cause; see the relief valve guide |
| Drain valve | Valve not fully closed, sediment on the seat, or a worn valve | Towel at the spout and the threads behind it | Repair (close, flush or replace) |
| Electric element panel | Element gasket or thread leak | Water seeping from under the panel cover | Repair (gasket replaced, threads resealed) |
| Burner area or under the tank (gas) | Combustion condensation on a cold tank | Stops once the tank is hot; the 8-hour pilot test | Normal if it stops; excessive amounts need a check |
| Tank body, seams or bottom | Corrosion through the steel tank | Every fitting dry and condensation ruled out | Replace |
| Welded fitting (spud) itself | Weld seeping where a pipe or valve meets the tank | Water at the weld, not the threads | Replace |
Sources: A.O. Smith Use & Care Guide 100366722 (2023), “Leakage Checkpoints”; A.O. Smith Technical Bulletins 15, 51 and 52. Tankless and heat pump models are covered further down.
For what each repair typically costs, and how age and warranty change the call when the part is fixable, see repair or replace.
Leaks from the top of the tank are usually fixable
Supply connections and pipe nipples
The hot and cold lines connect to short threaded pipes (nipples) in the tank top, often dielectric nipples with a plastic lining that isolates copper house piping from the steel tank to reduce galvanic corrosion. A.O. Smith lists corroded threads and bad thread seals as common fitting leaks; both are routine repairs. A cold pipe that is wet along its whole length is usually sweating, not leaking: A.O. Smith notes condensation can run down the cold supply pipe in warm or humid locations.
Relief valve threads and the anode port
A wet swab where the relief valve or anode rod enters the tank means the thread seal has failed. A.O. Smith’s fix is to drain the tank, remove the fitting and reseal it, which is a plumber’s job because it means draining hot water and resetting a safety device. Water at the weld around the fitting (the spud) is different: A.O. Smith says spuds “are welded to the tank and are not repairable,” so the heater is replaced.
Water at the draft hood or vent
Water dripping from the draft hood of an atmospheric gas heater, or the blower of a power-vent model, is condensed flue gas. A.O. Smith’s manual says it “is caused by a problem in the vent” and to contact the gas utility; its undersizing bulletin warns that excessive condensation can “produce a carbon monoxide hazard.”
Relief valve and drain valve drips
Water from the end of the relief valve’s discharge pipe means the valve is opening, which is its job. A.O. Smith says intermittent weeping usually means thermal expansion in a closed system, and a large burst of very hot water means a thermostat malfunction. Both need a diagnosis, not just a new valve. Never cap, plug or remove it. See relief valve leaking or dripping.
A dripping drain valve is often just not fully closed; A.O. Smith’s first step is to close it firmly by hand. If it still drips, sediment may be holding it open: the 2023 manual says to back-flush the valve and replace it if necessary. Water at the threads behind the valve is a reseal job.
Water under an electric element panel
Electric tanks have one or two heating elements screwed into the side of the tank, each sealed with a gasket behind an access panel. Water seeping from under a panel usually means a gasket or thread leak. A.O. Smith says the gaskets can be replaced and the threads resealed, so it is a repair, but one for a technician: it means shutting off power, draining the tank and working beside live terminals.
Electric tanks burn no fuel, so they make no combustion condensation. Water at the base of an electric tank with dry fittings and panels points to the tank or something nearby.
Water at the bottom: condensation or a failed tank
This is where condensation fools people most. Burning gas makes water vapor: A.O. Smith says about half a gallon per hour of burner operation. When cold water chills the tank, some condenses and drips onto the burner (you may hear sizzling) or the floor. A.O. Smith’s 2023 manual says this usually happens when a new heater is first filled, on high-efficiency models, or after heavy use with very cold refill water, and that it can be “diagnosed as a ‘tank leak’.”
| Clue | Condensation (gas tanks) | Tank leak |
|---|---|---|
| When it appears | While the burner runs or right after heavy hot-water use | Any time, including with the burner off |
| Heater type | Gas only; worst on new, high-efficiency or undersized heaters | Gas, electric or heat pump |
| Once the tank is hot | Stops: about 1–2 hours, or above about 110–115°F | Keeps coming |
| 8-hour pilot test | Floor stays dry | Floor is wet again |
| What to do | Nothing if it stops; ask about sizing or venting if it’s heavy every day | Shut off the water; plan a replacement |
Sources: A.O. Smith Technical Bulletins 15, 42 and 51; A.O. Smith Use & Care Guide 100366722 (2023). Rheem warns a failing tank may suddenly release more water.
A.O. Smith’s 8-hour test
Wipe up all the water
Under and around the heater, and in the drain pan.
Turn the gas control to “Pilot”
The main burner stops, so no new condensation forms. Many power-vent and electronic-ignition models have no Pilot setting; check your owner’s manual for its equivalent, or ask a technician to run the test.
Wait 8 hours
Avoid using hot water if you can.
Check again
Dry means it was condensation. Water means a leak: recheck every fitting, and if all are dry, A.O. Smith says the tank is leaking and the heater should be replaced.
Some condensation is normal. A.O. Smith says excessive condensation is not, and corrodes the flue and burner. If your heater drips after every morning’s showers, ask whether it is too small; see choosing the right size.
Tankless water heaters: connections, relief valve and condensate
- Connections and service valves below the unit. The isolation valves and unions on the hot and cold lines are threaded joints like any other. Use the same paper-towel test, and note whether the drip follows hot-water use.
- Pressure relief valve. Rinnai’s manual requires one on every installation and says periodic discharge “may be due to thermal expansion in a closed water supply system.” Don’t plug it.
- Condensate line (condensing models). Condensing units drain condensate through a trap, often through a neutralizer that Rinnai sells to raise its pH before it reaches the drain. Rinnai says water dripping from the condensate drain means it is working; if the line clogs, the trap can back up and the unit shows a code (code 10 on Rinnai covers a full condensate trap). The drain must be piped separately from the relief valve and from any air conditioner drain.
- Freezing. A unit outdoors or in an unheated space can split a pipe or heat exchanger in a hard freeze. Rinnai and Rheem both exclude freeze damage from warranty.
- Water from inside the cabinet. That is a technician job. The heat exchanger is the expensive part; Rheem warrants it for 15 years on its residential gas tankless models but excludes leaks caused by scale or a corrosive atmosphere.
For fault codes by symptom, see tankless problems and error codes.
Heat pump water heaters: check the condensate line first
A heat pump water heater pulls heat from the surrounding air and wrings water out of it, like a dehumidifier. The water collects in a pan under the evaporator coil on top and leaves through a ¾-inch condensate line. Rinnai’s manual says the condensate is non-acidic, needs a pump rated at least 2 gallons a day where there’s no gravity drain, must not empty into the water heater’s drain pan, and the line may need insulation so it doesn’t sweat.
- Water around the top or running down the jacket: a clogged or disconnected condensate line, or an overflowing pan. Rinnai’s troubleshooting starts with clearing the line; its units show a condensate-leak code.
- Higher electric bills along with the leak: Rheem’s service bulletin says a blocked condensate line can make the heater fall back to its electric elements.
- Water from the tank, fittings, relief valve or drain valve: everything in the tank sections above applies, because the bottom of a heat pump heater is an ordinary electric tank.
When the water isn’t coming from the heater
A.O. Smith’s leak checklist ends with a reminder that “leakage from other appliances, water lines, or ground seepage should also be checked.” Water heaters often share a basement, garage or closet with other things that drip:
- Furnace or air conditioner condensate. ENERGY STAR notes a plugged condensate drain can cause water damage. Water that appears only when the AC or furnace runs is a strong clue.
- Sweating cold pipes in humid weather, dripping at the lowest point.
- A washer, softener, filter or expansion tank nearby, with their own hoses and connections.
- A floor drain backing up or groundwater seeping in after heavy rain.
What to do while you wait for a plumber
If the tank is leaking or you can’t stop the water, close the cold-water valve at the heater and turn the gas control to Off or the breaker off; on an electric heater, cut power before the tank can lose water so the elements don’t run dry. Draining and the full checklist are in water heater emergency.
Before the plumber arrives
- Photograph the leak and the rating plate with model and serial number (Rheem suggests both)
- Note where water first reappeared after drying, and when
- Look up the warranty by serial number; see how old is my water heater
- If a gas heater’s burner area was under water, say so: A.O. Smith says a flooded heater must be replaced, not repaired
For the next heater, A.O. Smith recommends a metal drain pan piped to a drain where a leak could cause damage, plus a leak detector or automatic shutoff. Pan rules vary by code; see code requirements.
Common questions
Why is my new water heater leaking?
Often it isn’t. A.O. Smith’s manual says a new gas heater filled with cold water forms condensation that drips onto the burner or floor and should stop within about 1–2 hours of the water warming up. If water keeps appearing after that, check the pipe connections the installer made and the relief valve before suspecting the tank.
Can a leaking water heater tank be fixed?
No. A.O. Smith says leaking heaters “cannot be ‘repaired’,” and Rheem says replacement is the only safe option once a tank corrodes through. Leaks at threaded fittings, gaskets, valves and pipe connections are a different matter and are usually repairable.
Is it safe to use a leaking water heater?
A slow drip from a pipe joint or drain valve can usually wait a day or two with towels and a pan. A leak from the tank itself, water reaching electrical parts, or water from the vent cannot: shut off the water and the gas or power and call a plumber. Rheem warns that a failing tank may suddenly release more water.
Why is my water heater leaking from the top?
Usually a pipe connection, a thread seal where the hot, cold, anode or relief valve fitting enters the tank, or a cold pipe sweating in humid weather. All are fixable. Water at the weld around a fitting is the exception: A.O. Smith says welded fittings aren’t repairable.
Why is there water in my water heater’s drain pan?
A.O. Smith lists three usual causes: a leaking fitting, condensation, or a pinhole leak in the tank. Dry the pan, run the paper-towel and cotton-swab checks on the fittings, and on a gas heater try the 8-hour pilot test before deciding.
My heat pump water heater is leaking. Is the tank bad?
Check the condensate line first. A heat pump heater makes water as it cools the air, and a clogged or disconnected line can overflow its pan. Rheem says a blocked line can also make the heater fall back to its electric elements. If the condensate system is dry, check the tank fittings as you would on any electric tank.
Sources
Sources checked October 4, 2026. Prices, codes and rebates change. Check current details with your installer and local permit office.
- Installation Instruction and Use & Care Guide, residential power-vent gas water heaters, 100366722 Rev A (February 2023) ↗ · A.O. Smith, hosted by Lowe’s
- Residential gas water heater instruction manual 196293-002 (2004; leakage checkpoints for atmospheric models) ↗ · A.O. Smith
- Technical Bulletin 15: Condensation ↗ · A.O. Smith
- Technical Bulletin 51: Puddle on floor ↗ · A.O. Smith
- Technical Bulletin 52: Leaking temperature and pressure relief valve ↗ · A.O. Smith
- Technical Bulletin 45: Thermal expansion ↗ · A.O. Smith
- Technical Bulletin 42: Undersizing ↗ · A.O. Smith
- Technical bulletins index (leaking group) ↗ · A.O. Smith
- 5 Signs Your Water Heater Is Going Bad (December 2025) ↗ · Rheem
- What to Do Before Calling a Plumber or Replacing Your Water Heater (December 2025) ↗ · Rheem
- Technical Service Bulletin A108: Blocked condensate line (heat pump water heaters) ↗ · Rheem
- Residential tankless gas water heater warranty guide ↗ · Rheem
- Tankless water heater installation and operation manual 100000773 (SENSEI RSC) ↗ · Rinnai
- Electric heat pump water heater manual 100000867 ↗ · Rinnai
- T-575 galvanized steel dielectric nipple submittal sheet ↗ · Legend Valve
- Heating and cooling maintenance checklist ↗ · ENERGY STAR
- Water heater installation cost guide (installed price ranges) ↗ · Home Depot