A leaking water heater is not a problem that waits. Where the water is coming from tells you how worried to be: a drip from a fitting at the top is usually a quick fix, while water pooling under the tank often means the tank itself has rusted through, and that unit is done.
This guide walks through every place a water heater leaks from, what each one means, whether you can fix it yourself, and when to shut things down and call a plumber. Start with the emergency check below, then find your leak.
Find Your Leak
Is a leaking water heater an emergency? Sometimes. Treat it as urgent and shut things down if you see any of these: water spraying or running steadily rather than dripping, water pooling near electrical outlets or the burner, the tank visibly bulging, or a gas smell. Loud popping or rumbling usually points to sediment buildup rather than the leak itself, but it is a sign the unit needs service soon.
To shut a leaking heater down: turn off the cold water supply valve at the top of the tank. On an electric unit, switch off its breaker. On a gas unit, turn the gas control knob to “Off.” Then open a hot tap somewhere in the house to relieve pressure. A slow drip from a fitting can usually wait for business hours; anything wetting the floor should not.
TOPLeaking From the Top or the Connections
OFTEN DIY-ABLEA leak at the top of the heater is the one you most want to find, because it almost always traces back to a fitting rather than the tank. Run your hand along the two pipes entering the top of the unit and the area around them. If they come away wet but the tank below stays dry, you are dealing with a connection, not a failed tank.
Loose or corroded inlet and outlet fittings. The cold-water inlet and hot-water outlet are threaded connections, and they work loose over years of the tank heating and cooling. Dry everything, then watch where the bead of water reappears. A nut that has backed off a quarter turn can usually be snugged with a wrench. If the threads are green with corrosion, the fitting needs to come apart, get cleaned, and be resealed.
A failing T&P discharge or nipple. Heat-trap nipples and dielectric unions sit right at the top and are common culprits. They are inexpensive parts, but replacing one means draining the tank and breaking the connection, which is firmly in plumber territory unless you are comfortable with that work.
Can you fix it yourself? Tightening a loose fitting, yes. Anything that needs the connection opened up is worth a call, because a sloppy reseal here turns a small drip into a steady one.
T&PLeaking From the T&P Relief Valve
SAFETY VALVEThe temperature and pressure relief valve is the brass valve on the side or top of the tank with a pipe running down toward the floor. It is a safety device, so a leak here is worth understanding rather than just stopping.
If water is dripping from the discharge pipe, the valve is doing its job because something pushed the tank past a safe limit. The usual reasons are a thermostat set too high, which builds excess pressure as water expands, or high incoming water pressure from the street. Thermal expansion in a closed plumbing system, common where a backflow preventer or pressure-reducing valve is installed, will also trip it and points to a missing or waterlogged expansion tank.
Sometimes the valve itself has simply worn out and weeps even at normal pressure. You can test it by lifting the lever briefly to flush out grit, but if it keeps dripping afterward, replace it. The U.S. Department of Energy recommends testing the T&P valve every six months as part of routine maintenance.
Do not cap or plug this pipe. The discharge line has to stay open. If the valve is releasing because of pressure or temperature, blocking it removes the one safeguard standing between you and a dangerous tank. Replacing the valve is doable for a confident DIYer, but figuring out why it is releasing is what actually solves the problem, and that is worth a professional eye.
DRAINLeaking From the Drain Valve
OFTEN DIY-ABLEThe drain valve sits near the bottom of the tank, where you would hook up a hose to flush sediment. It looks a lot like a hose bib. Because it is at the lowest point, a drip here is easy to mistake for the tank itself leaking, so confirm the water is coming from the valve and not from the seam above it.
Most drain valve leaks come down to one of two things. The valve was not closed fully after a flush, or a bit of sediment is holding it open. Try closing it firmly, and if it still drips, open it briefly to let any debris wash through, then close it again. The other cause is an old plastic valve that has simply degraded; those are notorious for weeping after a few years.
Can you fix it yourself? A quick fix is a brass hose cap threaded onto the outlet to stop a minor drip. Swapping the valve is a bigger job that means draining the tank, and a stubborn old valve can fight you, so many people hand this one off.
BOTTOMLeaking From the Bottom of the Tank
REPLACE / CALL A PROThis is the leak nobody wants. If you have ruled out the drain valve and the fittings above, and water is still collecting under the unit, the tank has very likely corroded from the inside out. The steel tank is glass-lined, and once that lining cracks and the anode rod that protects it is used up, rust eats through the wall. There is no patch for that.
A few signs point this way. The water shows up only at the base and seems to seep from under the outer jacket rather than from any visible fitting. You may see rust staining around the bottom edge. The leak often gets worse as the tank fills and heats, then eases as it cools, because the expanding water is pushing through the failure point.
Can a leaking water heater be repaired? A leak from a valve, a fitting, or a connection, yes, those are repairs. A leak from the tank body itself, no. When the tank wall has gone, the unit needs to be replaced, and trying to limp it along risks a full rupture that empties dozens of gallons onto the floor. If you are weighing your options, our guide on whether to repair or replace your water tank walks through the math.
Manufacturers like Rheem and A.O. Smith put the typical life of a tank water heater at eight to twelve years, so if yours is in that range, replacement is the sensible call regardless. A few other symptoms tend to show up around the same time; here are 10 signs it’s time for a water heater replacement.
TANKLESSLeaking Tankless Water Heaters
VARIESTankless units leak differently because there is no big storage tank to rust through. Water inside the wall-mounted cabinet usually traces to the fittings where the plumbing connects, the isolation valves used for flushing, or the internal heat exchanger.
Connection and valve leaks are the friendlier outcome and often just need a fitting tightened or a worn gasket replaced. A leaking heat exchanger is the serious one. Hard-water scale is the usual reason it fails, which is exactly why annual descaling matters on these units. The Department of Energy notes that periodic maintenance meaningfully extends a tankless unit’s life. If the exchanger has cracked, repair is rarely worth it against the cost of the part and labor, and replacement is often the better value.
If your tankless unit is also showing an error code along with the leak, that code narrows things down fast. Our water heater error code guide covers what each one means across Rheem, Navien, Rinnai, Noritz, and the rest.
What to Do Right Now (and Who to Call)
Whatever the source, the first moves are the same. Shut off the cold water supply at the top of the tank to stop more water from feeding the leak. Kill the power at the breaker on an electric unit, or set the gas control to “Off” on a gas unit, so the heater is not firing against a draining tank. Then mop up standing water and keep it away from outlets and the burner area.
From there, match the fix to the source. A loose fitting or a drain valve left cracked open you can often handle yourself. A relief valve that keeps releasing, a connection that needs to be opened and resealed, or water coming from the tank body all call for a licensed plumber, both to do it right and to tell you honestly whether the unit is worth saving. If your electric unit also stopped making hot water, our electric water heater troubleshooting guide can help you narrow it down.
Who do you call for a leaking water heater? A licensed plumber or a water heater specialist. For a leak that is actively flooding, call right away and mention it is an active leak so they treat it as urgent. For a slow drip, you have time to schedule, but do not let it sit for weeks; small leaks rarely get smaller, and water against the base of the tank only speeds up corrosion.
Quick Reference: Leak Location, Cause & What to Do
| Where it’s leaking | Likely cause | Urgency | What to do |
|---|---|---|---|
| Top / inlet & outlet | Loose or corroded fitting | Low to moderate | Tighten if loose; reseal or replace fitting |
| T&P relief valve | Excess pressure/temp, thermal expansion, or worn valve | Moderate | Find the cause; never cap the pipe; replace valve if it weeps |
| Drain valve | Not fully closed, debris, or worn plastic valve | Low | Close firmly, flush debris; cap or replace the valve |
| Bottom of tank | Internal corrosion / tank failure | High | Shut it down; replace the unit (not repairable) |
| Tankless cabinet | Fitting/valve, or cracked heat exchanger | Moderate to high | Tighten fittings; exchanger failure usually means replace |
Still Not Sure Where It’s Coming From?
Leaks can be deceptive. Water travels along pipes and runs down the side of the tank before it drips, so the puddle on the floor is not always under the actual source. If you have dried everything off and you still can’t pin down where the water starts, that is a good moment to bring in someone who looks at these every day. Catching a small leak early is almost always cheaper than dealing with the water damage a missed one causes.
Water on the floor? Let’s get it handled.
Our team has been diagnosing and fixing water heater leaks for decades. Whether it’s a quick valve swap or a full replacement, we’ll tell you straight what your unit needs.
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