Water Heater Drain Valve Leaking

Is it really the drain valve?

The drain valve sits near the bottom of the tank, on the front. On most residential heaters it's a plastic or brass valve with a hose thread on the outlet. Water near the bottom of the heater can come from several places, so confirm the source before you buy parts.

Dry everything with a towel. Then hold a dry paper towel under the valve outlet, then under the threads where the valve enters the tank, then along the bottom seam of the tank. Wait a few minutes between each check. Also look up: water from a leaking fitting on top can run down the side and drip off right next to the valve.

• Dripping from the hose outlet: the valve isn't sealing. Start with the easy fixes below.
• Weeping around the threads where it enters the tank: the threaded joint is leaking. Tightening sometimes helps; replacement usually does.
• Water coming from behind the jacket or the bottom of the tank: the tank is leaking. See water heater leaking from the bottom.

Likely causes

1. 1

   Cause 1: The valve isn't fully closed

   This happens after someone flushes the tank or tests the valve. Turn the handle or slotted stem clockwise until it stops. Plastic valves don't need force; cranking on them cracks the body. A.O. Smith's first fix is simply to make sure the drain valve is completely closed.

2. 2

   Cause 2: Sediment stuck in the seat

   Every tank collects sediment, and the drain valve sits right where it settles. A grain of scale under the washer keeps the valve from sealing. Attach a garden hose, run the other end to a floor drain or outside, and open the valve fully for a few seconds to blast the debris out. Close it again. This often stops the drip completely.

3. 3

   Cause 3: A worn-out valve

   Plastic drain valves get brittle with heat and age, and their washers flatten. If the drip continues after a flush, the valve is done. Brass replacement valves cost little and hold up better.

4. 4

   Cause 4: A leaking threaded connection

   If water seeps from the threads where the valve screws into the tank, the joint sealant has failed. Snugging the valve a little can stop it, but a plastic valve can crack if you overdo it. HomeGuide notes that leaks from a fitting, bolt or drain valve may only need tightening.

Quick fix: cap it

If the valve drips from the outlet and you can't replace it today, screw a brass garden hose cap with a good rubber washer onto the outlet. It's a stopgap. It holds the water in, but the valve is still failing, so plan the replacement.

How to replace a water heater drain valve

1. Turn off the power or set the gas valve to off.
2. Close the cold water supply valve on top of the heater.
3. Open a hot water tap upstairs to let air into the tank.
4. Connect a hose to the drain valve and drain the tank to a floor drain or outside. Our water heater drain guide has the full routine.
5. Unscrew the old valve. Plastic valves sometimes break at the threads; a pipe extractor or a plumber can get the stub out.
6. Wrap the new valve's threads with PTFE tape, or use pipe dope, and thread it in snug with the outlet pointing down.
7. Close the valve, close the upstairs tap, and turn the cold supply back on. When water runs from a hot tap without air, the tank is full.
8. Check the new valve for drips, then restore power or relight the pilot.

If the old valve breaks off inside the tank, or the tank is old and the threads are rusted, stop and call a plumber. Forcing it can turn a valve job into a replacement.

When it's the tank, not the valve

Water from the bottom seam or from under the jacket means the steel tank has rusted through. A.O. Smith says a tank that corrodes and leaks usually means the entire water heater needs to be replaced. There's no patch for it. HomeGuide puts the cost of replacing a leaking tank heater at $600 to $1,800. Check water heater replacement cost for the full picture.

When to call a plumber, and what it costs

Call a plumber if the valve breaks off, the threads are corroded, the leak comes from the tank, or you'd rather not drain a tank full of hot water. HomeGuide puts water heater leak repair at $100 to $1,000 depending on the source. A valve swap is a small job compared with a tank leak. Expect a service call fee of $50 to $200 in many areas.

A drain valve job is a good time to flush the tank. HomeGuide puts a professional flush at $75 to $200, and A.O. Smith recommends draining a few gallons once a year to clear sediment.