Like all water valves, the drain valve on your water heater can wear out and leak. Often this happens after you drain the water heater as part of the regular maintenance of the unit, but it can happen anytime. While you can repair similar valves, such as garden spigots, it's not a good idea to attempt a repair on a water heater drain valve; if the repair isn't successful, you'll have water leaking into your house.
Replacement drain valves are readily available and easy to install. Just make sure to use a new valve that matches the old one. You can buy valves through online appliance parts dealers (using your water heater's model number), or simply take the old valve into a local home center or plumbing supplier to find an exact replacement.
How to Replace a Water Heater Drain Valve
The drain valve holds back all the water in the tank so, for obvious reasons, you must drain the tank completely before removing the old valve. Follow all of the necessary steps for shutting down your water heater before draining the tank. This ensures that the tank burner (for a gas heater) or elements (for an electric heater) won't turn on while the tank is draining.
- Turn off the power to an electric water heater by switching off the appropriate breaker in the home's electrical service panel (breaker box). Turn off the gas to a gas water heater by turning the pilot knob to the PILOT setting. This will prevent the burners from igniting but should keep the pilot light running so you don't have to restart it later. Alternatively, shut off the gas supply by closing the valve on the gas line near the water heater.
- Close the valve on the cold water supply pipe leading to the water heater. There should be a valve on the line near the top of the heater tank.
- Connect a garden hose to the water heater's drain valve, and run the hose to a nearby floor drain or outdoors.
- Open the drain valve all the way to begin draining the tank. Some valves have handles; others have a slotted spindle that you turn with a flathead screwdriver.
Warning: The water draining from the tank will be hot.
- Open the temperature and pressure relief valve (T&P valve) on the side or top of the tank by flipping the lever to the open position. This allows air into the tank to prevent suction that would inhibit draining.
- Let the tank drain completely, then close the T&P valve by flipping down its lever and letting it snap back to the closed position.
- Remove the hose from the drain valve. Remove the drain valve by turning it counterclockwise with a large adjustable wrench, pipe wrench, or tongue-and-groove pliers.
- Wrap the threads of the new valve with plumber's tape and thread it into the tank by hand. Tighten the valve with a wrench, stopping when the valve outlet is pointing downward in the same position as the old valve. Confirm that the valve is completely closed.
- Open the hot-water tap on any faucet inside the house.
- Open the valve on the cold water supply line to begin refilling the tank. When water flows out of the faucet, the tank is full, and you can close the faucet. Tip: Run all of the faucets in the house briefly to expel air from the water lines; the air and water will spurt loudly, so it's best to do this now and not be surprised by it later.
- Turn on the power to an electric heater, or turn the pilot knob to ON for a gas heater. The water heater will begin heating the water in the tank. If necessary, relight the pilot following the manufacturer's directions.
- Check the new drain valve for leaks, checking again periodically for the next day or so, just to make sure there are no problems with the valve.