Is the water heater leaking, or is it a fitting?

Water on the floor near a heater is one of four things: a joint or a valve you can see, condensate or sweat that is not a leak, the relief valve doing what it was built to do, or the steel tank itself. Only the last one means the heater is finished.

The expensive mistake is to replace a tank because the drain valve weeps, or to “fix” a split tank with a clamp because the quote was unpleasant. This page is the separation test. A relief valve that drips on its own schedule, with the rest of the heater dry, is why the relief valve drips. Do not cap it while you think.

Stop. If water is falling fast enough to reach outlets or the electrical panel path, shut the cold-water inlet on top of the heater, or the house main, if you can do it from a dry place.

For an electric heater, turn the breaker off only if you can reach the panel without standing in water. Gas shutoff is the valve on the gas line, turned perpendicular to the pipe on a typical quarter-turn valve.

Then call a plumber. Diagnosis can wait until the water has stopped.

Dry it, then make the heater work

Mop the jacket, the pan, the valves, and the floor until they are dry. Wrap a paper towel around the cold inlet, the hot outlet, the drain valve, and the relief-valve body.

Run hot water at a faucet so the heater fires, and watch for twenty minutes. A leak declares itself. Condensation often does not, or it declares itself only while the burner is on and the tank is still cold.

Condensation on the outside of a cold tank in a humid room is ordinary. The jacket sweats, the sweat runs to the floor, and it looks like a leak at the base. It stops once the tank is hot and the room dries out.

A new or high-efficiency gas heater can also drip from the flue area during the first minutes of a burn, because water vapor in the exhaust condenses on a cold flue surface. That drip ends when the heater is fully up to temperature.

A storage tank that is truly leaking does not stop when the steel is hot. If the paper towel at the fittings stays dry and the only moisture is a film on a cold jacket in July, you do not have a failed tank.

Improve ventilation and, if the tank is old and poorly insulated, consider whether the insulation is soaked. Soaked insulation stays wet and hides corrosion. That is a reason to look harder, not a reason to ignore a puddle that returns every morning.

Condensing gas heaters are supposed to make liquid. That liquid belongs in the condensate drain, not on the burner deck. If the trap or the hose has come off, you will see water and you will sometimes see a lockout.

Re-seat a hose that has popped off a barb, if that is obviously all that happened. Do not reroute acidic condensate into the relief-valve pipe. The difference between heat-pump condensate and gas-heater condensate is in condensing gas heaters and the heat pump guide.

Fittings, nipples, and the drain valve

The threaded connections on top are the first place to look, because they are outside the steel shell. A loose flexible connector, a failed washer, or a pitted dielectric nipple drips down the jacket and fools you into thinking the leak is lower than it is. Dry the top with the water off and the pressure relieved, then watch.

If the drip is at a union you can reach, and the tank port itself is not pitted, a plumber or a careful homeowner who already does plumbing can remake that joint. If the nipple is the steel of the tank and the threads are rotten, tightening will make it worse.

The repair is often a new heater, because the port and the tank are one corrosion story. The anode is what was supposed to prevent that story. On a tank that has already lost a port, a new anode is late.

Element gaskets on electric heaters leak at the access openings, usually after an element change. The tell is water at the element flange and a dry base elsewhere.

The repair is a new gasket with the power proved dead and the tank drained below that element, then a complete refill before power. Dry-firing the new element is the sequel nobody wants. Electrical safety covers the sequence.

The drain valve at the bottom is a plastic petcock on a great many residential tanks. Sediment holds it off its seat.

A hose-thread cap is not a repair you should trust, and it is not a substitute for a valve that closes.

Flushing, described in how to flush a tank, sometimes clears the debris and lets the valve seal.

Sometimes the valve then will not close at all. Be ready for that before you open a drain valve on a tank you cannot isolate. Replacing the valve means draining the tank and working at a low threaded port.

If the port threads come out with the valve, the tank is done. That is a known way a “simple valve swap” becomes a replacement. Price both before you start if the tank is old.

The shell leak

Water from under the jacket, from a seam, from a rust bloom that bubbles paint, or from the underside when every fitting towel stays dry is tank water. The glass lining has a hole, the steel behind it is perforated, and no sealant, epoxy, or hose clamp restores a pressure vessel.

Shut the cold inlet so makeup water stops feeding the leak. Shut gas or power. If the leak is slow you may still have time to let a plumber do this. If it is fast, you do it now and mop later.

Do not keep using a leaking shell “until the new one arrives” if the water is reaching electrical equipment or if the heater is gas and the burner area is flooded. Water in a gas burner is a carbon monoxide and fire problem, not only a flooring problem.

The pan, if you have one and if it is drained, buys time for a slow leak. Many pans are undrained and simply become a shallow pool that overflows at the same rate as the leak. The pan requirement where damage would result is in permits, pans, and straps. A pan does not turn a split tank into a repair.

Internal leaks are why the age of the tank matters in repair or replace. A six-year-old tank with a leaking element gasket is a repair. A twelve-year-old tank with a wet jacket and a dry top is a replacement.

Ask the plumber to say which of the four categories they see. “It might be the tank” is not a diagnosis. Dry towels and ten minutes of watching are a diagnosis.

What people call a leak and should not

A temperature-and-pressure valve that opens will wet the floor if its discharge pipe is missing or if it terminates in the pan. The valve may be doing the only safe thing available to it. Fixing the path, the expansion tank, or the failed valve is the dripping relief valve article. Plugging the valve so the floor stays dry removes the last safety device on the tank.

Rusty water at the tap, with a dry floor, is not a leak. It is corrosion products leaving through the plumbing.

That is discolored water. It often means the anode is gone and a leak is in your future. It is not the leak yet.

Checklist: name the water before you buy a heater

• Stop a fast leak at the cold inlet or the house main. Kill power from a dry place.
• Dry every surface. Tag the inlet, outlet, drain, element flanges, and relief valve with paper towels.
• Fire the heater or draw water so it works. Wait.
• Moisture only while cold, then dry: sweat or flue condensate. Confirm it actually stops.
• Towel wet at a joint, tank port sound: remake the joint.
• Towel wet at the drain valve: flush debris or replace the valve, knowing the port can fail.
• Water from the jacket with dry towels above: shell leak. Replace the heater. Do not seal it.
• Water only from the relief discharge: leave this page for the relief-valve guide. Do not cap the pipe.

After a shell leak, replace the anode habit on the new tank, add a pan and a drain if the location can damage the house, and add an expansion tank if the plumbing system is closed. Otherwise the new relief valve will drip and you will be back here in a month, blaming the new heater for a plumbing condition the old heater already had.

Sources

International Code Council, “CodeNotes: Water Heater Safety in the I-Codes,” and IRC P2801 and P2804 as adopted locally, for pans and relief-valve discharge. Manufacturer installation manuals for condensate versus leak warnings on high-efficiency models (A. O. Smith, hotwater.com; Rheem, rheem.com; Navien, navieninc.com). U.S. Department of Energy, Energy Saver, storage-heater service life in “Which Water Heater Is Right for You?”