Water heater drain valve leaking: causes and fixes

Make sure it's really the drain valve

Dry the valve and the tank around it, then watch. Water that appears at the valve's outlet or around its stem is the valve. Water that runs down the tank from above is something else, often the relief valve pipe or a top fitting. Water that seeps from under the tank's jacket with the valve dry is more serious. See water heater leaking from the bottom.

Not fully closed

Bulletin 51's first step is to check that the valve is closed tightly. Many residential drain valves open with a handwheel or a flat screwdriver slot. Turn it clockwise gently until it stops. Don't force a plastic valve, which can crack.

Sediment in the seat

This is the classic drip right after someone has flushed the tank. Bradford White calls the water heater the home's main water reservoir, where rust, sand and clay from the incoming water settle over the years. When the valve is opened, that grit rushes through it, and a small piece can stop it from sealing.

Opening the valve fully for a few seconds with a hose attached can clear the piece, then close it again. A. O. Smith's draining guide warns that sediment can also clog the valve so water won't come out at all, and says to call a plumber in that case.

Sediment is heavier after water main work or in homes on wells. Bridgewater, Massachusetts has told residents to run cold water until clear and avoid hot water during discoloration (see our Bridgewater page), and Pembroke advises flushing from an outside faucet near the meter (see our Pembroke page). Both steps help keep grit out of the tank and away from the drain valve.

A worn or cracked valve

If the drip continues with the valve closed and flushed, the seal or body is worn. A. O. Smith's leak guide says a faulty drain valve is usually fixed by tightening it or replacing it. Many tanks come with a plastic valve. Rheem sells a brass full-flow replacement that it says fits most major brands, and full-flow valves pass sediment more easily during a flush.

Replacing a drain valve

A. O. Smith's steps for draining a tank are the same first steps: turn off the power or set the gas to off, let the water cool for a few hours, close the cold water supply, open a hot tap, and drain through a hose. The valve then unscrews from the tank and the new one goes in with thread sealant.

On an older heater that has never been flushed, the tank can be heavy with sediment that keeps clogging the hose and the new valve. If the heater is 10 or more years old and leaking from the drain valve, compare the repair with a new heater before you start.

Until it's fixed, a brass hose cap screwed tightly onto the valve outlet stops most drips. Keep a pan or towel under it and check it daily.

Local pages mentioned

• Pembroke, MA
• Bridgewater, MA