Water Heater Leaking: What to Check and What to Shut Off

Order matters, because a heating element or burner running against a draining tank can burn out, and the cold-water valve controls how much water keeps arriving.

1. Electric heater: switch off the breaker. Gas heater: turn the gas control to off, or to pilot if the dial offers only that, and close the gas shutoff valve if it is within reach.
2. Close the cold-water inlet valve on the pipe above the tank, turning it clockwise until it stops.
3. Open a hot tap somewhere in the house so the tank does not pull a vacuum and the leak slows.
4. If the leak is heavy, attach a hose to the drain valve and run it to a floor drain or outdoors; let the tank empty.
5. Take photos before cleanup, then mop and place towels or a wet vac. In an attic, check the ceiling below for staining.

Leaks look similar but come from different places, and the location tells you whether the heater is finished. Trace the water upward with a dry paper towel, because it runs down the tank and pools at the bottom no matter where it starts.

A leak at the bottom is usually the end of the tank. Rust has eaten through the inner steel lining or a weld, and no patch holds under the heat and pressure of a working tank. Before concluding, rule out the drain valve, the T&P discharge and the pan line, all of which can mimic a bottom leak and are cheap to fix.

Check whether the wetness appears only after the heater runs, which can also point to thermal expansion in a closed system. Expansion forces water past the T&P valve and shows up as a steady drip from the discharge line, not the tank. An expansion tank cures that, as described in expansion tank installation.

A leaking fitting can drip for months. A leaking tank is different, and there is no safe timetable. Some seams weep slowly for days; others let go suddenly and empty 40 or 50 gallons. The tank body cannot heal itself, and corrosion at one pinhole widens with time.

Treat a confirmed tank leak as an immediate replacement. Shut off water at the heater, drain it and decide with the plumber whether the home can run without hot water until the swap. The repair-versus-replace guidance on water heater replacement covers the next step.

Many DFW homes from the 1990s and 2000s have the heater in the attic, above a bedroom or hallway ceiling. A slow leak there can stain drywall for weeks before anyone sees it, and a burst can bring down the ceiling. The drain pan and its line are the early warning; a pan that holds water is a sign the heater leaks. Check the ceiling below and the pan line outlet at the eave.

Slab homes route supply lines overhead or through the slab. A heater on the ground floor leaks onto the floor, which shows quickly, but hidden leaks under the slab appear as a hot spot on the floor or a spinning water meter with every fixture off.

Photograph the heater, the label with the model and serial number, the leak source and the damage before you clean up. Most Texas homeowner policies respond to sudden and accidental water discharge and not to long-term seepage or the failed heater itself, though terms differ, so read your policy or ask your agent before throwing anything away.

Dry wet drywall and insulation within a day or two, because mold can start within a couple of days. Wet insulation in an attic should be removed and replaced rather than dried in place.

Sediment from DFW hard water can foul the drain valve and the T&P valve, so a valve that was never exercised leaks when it finally opens. After a hard freeze, check the pipes and fittings around the heater for cracks as they thaw, as happened across the region in February 2021.