Water heater leaking from the top: where to look

Stop the water first

The building code calls for an accessible shutoff valve on the cold water pipe at or near every water heater. Close it to stop fresh water feeding the leak. Turn off the breaker on an electric heater, or set a gas heater's control to off or pilot. The water in the tank stays hot for hours, so keep your hands clear of the fittings until it cools.

Inlet and outlet connections

The two pipes on top carry cold water in and hot water out. A. O. Smith's leak guide says these connections can loosen over time from thermal expansion and wear, and then need tightening or replacing. Its Bulletin 51 adds a catch: in a warm or humid room, condensation can form on the cold pipe and run down onto the tank, which looks like a leak but isn't.

Wipe each fitting dry with a paper towel and watch which one gets wet first. A drip at a flexible connector or a threaded joint is usually a quick repair.

White or green crust: corroded nipples

The short threaded pipes screwed into the top of the tank are called nipples. Where copper pipe meets the steel tank, galvanic corrosion can set in. An NIH technical bulletin explains that it takes three things: two dissimilar metals, an electrolyte such as water touching both, and an electrical path between them. Dielectric fittings separate the metals to prevent it.

A crusty white, green or rust-colored build-up around a nipple usually means a slow leak has been seeping and evaporating for a while. A plumber can replace corroded nipples or add dielectric fittings. If the corrosion has eaten into the tank opening itself, replacement is the safer call.

Water chemistry plays a part too. Marshfield, Massachusetts treats its naturally acidic well water at every well, and in 2024 sampling 2 of 41 homes were above the copper action level (see our Marshfield page).

The relief valve

The relief valve sits on the top or upper side of the tank with a pipe running down toward the floor. Water at its threads is a connection leak. Water coming out of the pipe means the valve opened, usually from high pressure or thermal expansion. Our guide to a leaking relief valve walks through it. Never cap or plug that valve.

Shutoff valve, anode port and elements

The cold water shutoff valve can drip from its stem, especially right after it's been turned. Tightening the packing nut a little often stops it. The anode rod screws into a port on top of many tanks, and a leak there can mean the threads need resealing, or that the rod and tank are badly corroded. On electric heaters, Bulletin 51 notes that leaks from the element gaskets can be fixed by replacing the gaskets, and the element threads may need resealing.

High pressure behind it all

A. O. Smith says excessive water pressure stresses the heater and can cause leaks at the tank and the connections, and that a pressure-reducing valve or an expansion tank can fix it. A hose-bib pressure gauge costs little. Post Falls, Idaho reports average system pressure of 65 to 75 psi, higher in the south of town (see our Post Falls page).

Local pages mentioned

• Post Falls, ID
• Marshfield, MA