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.
Leaking from the top or the connections
Almost always a fitting, not the tank
A leak up top is the one you want, because it nearly always traces back to a fitting rather than the tank. Run your hand along the two pipes entering the top of the unit — if they come away wet but the tank below stays dry, you are looking at a connection.
The cold-water inlet and hot-water outlet are threaded joints that work loose over years of the tank heating and cooling. Dry everything, then watch where the bead of water comes back. A nut backed off a quarter turn can sometimes be snugged with a wrench.
Green, corroded threads, a failing heat-trap nipple, or a dielectric union mean the connection has to come apart, get cleaned, and be resealed. A sloppy reseal here is what turns a small drip into a steady one.
Tightening a loose fitting is safe; anything that opens the connection is worth a call. We reseal it right the first time — usually the same day.
Leaking from the T&P relief valve
A safety valve — never cap it
The 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 before you touch it.
If water drips from the discharge pipe, the valve did its job — something pushed the tank past a safe pressure or temperature. Lift the lever briefly to flush out grit. If it keeps weeping afterward, it needs attention.
Sometimes the valve has simply worn out and weeps at normal pressure; other times the real issue is the pressure or temperature behind it. Either way, replacing the valve or finding the cause is technician work.
Never cap or plug the discharge pipe. It is the one safeguard between a pressurized tank and a real failure. If it is flowing steadily, shut off the water and call right away.
Leaking from the drain valve
Looks like a hose bib, near the floor
The drain valve sits near the bottom of the tank, where you would hook up a hose to flush sediment. Because it is low on the unit, its drips are easy to mistake for a failing tank.
Most drain-valve leaks are the valve left not-quite-shut after a flush, or a bit of sediment holding it open. Snug it closed and see if the drip stops.
If it keeps dripping, the valve needs replacing — a job that means draining the tank. A brass hose cap threaded onto the outlet will stop a minor drip until we get there.
Swapping a drain valve is a tank-drain job we handle same-day.
Leaking from the bottom of the tank
The one nobody wants to find
This is the leak nobody wants. If you have ruled out the drain valve and the fittings up top and water is still collecting under the unit, the tank has likely corroded through from the inside.
The tell-tale signs: water shows up only at the base and seems to seep from under the outer jacket rather than from any visible fitting. That is the inner tank, not a part you can tighten.
A leak from a valve, a fitting, or a connection is a repair. A leak from the tank itself cannot be patched — it is a replacement. The good news is we can often swap it the same day. Here are the signs it is time to replace.
Leaking tankless water heater
No storage tank to rust through
Tankless units leak differently, because there is no big storage tank to rust through. Water inside the wall-mounted cabinet usually traces to the fittings, a valve, or the 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 bigger one, and it is firmly technician territory.
If the unit is also throwing an error code with the leak, that code narrows things down fast. Our error code guide covers every major brand.
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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