Water Heater Leaking From the Bottom or Top: What to Do Now

Work through these in order. None of them needs tools.

• Close the cold water supply valve, on the pipe going into the top of the heater. Turn a handle valve clockwise; turn a lever valve so it sits across the pipe. This stops more water from entering the tank.
• Gas heater: turn the control knob on the front to Off. Electric heater: switch off its breaker at the panel. A heater with no water coming in should not keep firing.
• If you cannot find or close the heater's valve, shut off the main water valve to the house.
• Move boxes and anything else off the floor, and put towels or a pan where the water is heading.
• Open a hot water faucet somewhere in the house. It relieves pressure in the tank and slows the leak.
• If you smell gas, leave the house and call 911 or your gas utility from outside.

Dry the area and watch. Where the water first appears tells you most of what you need to know.

From the top: the hot and cold connections, the short nipples screwed into the tank, the flexible supply lines and the anode port. These leak from corrosion or a loose joint, and most are repairable. Water running down the outside of the jacket from the top can look like a bottom leak, so follow it up.

From the side, out of a pipe: that pipe is the discharge for the temperature and pressure relief valve, the T&P valve. It drips when the valve opens to relieve pressure or temperature, or when the valve itself is wearing out.

From the bottom front: the drain valve, a small spigot near the base. A drip from its spout or around its stem is usually a worn valve or a cap that has worked loose.

From underneath, with everything above it dry: the tank. Steel tanks rust through from the inside, and once water seeps out of the bottom, the tank is done.

The T&P valve is a safety device. It opens if the tank pressure or water temperature gets too high, so the tank does not. A valve that drips after the heater runs often points to thermal expansion in a closed system, where a check valve or pressure-reducing valve keeps heated water from pushing back into the main. An expansion tank on the cold line is the usual fix. High street pressure can do it too.

A valve that blows steady hot water or steam is different. That means the heater may be overheating. Turn off the gas control or breaker, keep clear of the discharge, and call. Never cap, plug or shorten that discharge pipe. Old T&P valves that have stuck or scaled up get replaced.

One more thing that fools people: a gas tank filled with very cold water can sweat inside the burner area on first firing, and the drops sizzle on the burner. That condensation should stop once the tank warms up. Water that keeps coming after the tank is hot is a leak.

The plumbing code requires a tank water heater to sit in a drain pan wherever a leak would cause damage: attics, upstairs closets, above finished rooms. The pan has to be at least an inch and a half deep, with a drain of at least three-quarter-inch pipe to a floor drain or to outside. An existing water heater replaced where no pan drain was ever installed does not always have to add one, but in an attic it is still worth doing.

A pan is designed for drips and slow leaks. It will not contain a tank that splits, which is why the age of an attic heater matters so much. A water leak sensor in the pan, or an automatic shutoff valve on the supply, adds warning for a heater nobody looks at.

A leaking fitting, supply line, drain valve or T&P valve on a heater in good shape is a repair. A leak from the tank body is a replacement every time; there is no patch for a tank that has rusted through. If the heater is past 10 years and the repair is anything more than a valve, most owners are better off replacing it now than paying for a repair on a tank near the end.

Replacing a gas water heater is permitted work, because it involves the gas connection and the venting. We also check the relief valve discharge, the pan and the expansion tank so the new heater is not set up for the same failure.