How to Unclog a Drain Valve: When You Can’t Drain Your Water Heater

unclog drain valve

Knowing how to unclog a drain valve can save the day when you have 50+ gallons of hot water in your tank and it doesn't want to drain! The most common reason a drain valve clogs is from excessive sediment.

Sediment can enter your tank with the incoming water supply, and it also can be the remnants of the inside of your tank, such as rust. Sediment is even a byproduct of heated water - when water is heated the minerals separate and settle at the bottom of the tank, over time forming lime scale.

Sediment build-up is bad news for water heaters. It reduces the unit's efficiently, breaks down the interior of the tank, and has the potential to build to the point of clogging the drain valve. This is one of the reasons why performing regular maintenance on your water heater is so important. 

Is Your Drain Valve Clogged?

Unclogging a drain valve can range from an easy task to a major headache. Failure to find a way to drain your tank will eventually lead to the purchase of a new water heater since the inside of the tank will break down and an unrepairable leak will develop. 

But before jumping to conclusions, follow these steps to determine if your drain valve is in fact, clogged:​

  • First turn off the fuel to your water heater. Turn off the circuit breaker for electric units​ and turn the control knob to pilot or off on gas.
  • Attach a garden hose to the drain valve and run the other end outside or to a drain. Then open the drain valve.
  • Open a nearby hot water faucet to allow air to enter the tank.
  • Inspect the water as it drains from your tank. If it is clear, the valve is not clogged.
  • If the water isn't draining or is only slightly draining, it is obstructed and you'll need to unclog your drain valve.
  • In most cases the water within your tank will be hot and you'll need to take safety precautions to prevent being burned.
  • Wear safety goggles and work gloves to protect your eyes and hands when attempting to drain the tank.
  • Before attempting to drain your tank, always cool the water inside. See below

3 Methods to Cool the Water Within the Tank

  • Allow the water heater to sit for up to 24 hours after shutting off the power.
  • Drain as much water as possible thru the drain valve. Leave the water inlet valve open with the power off. As the water drains from the tank, cool water will enter and dilute the hot water. This method only works if your drain valve is not completely clogged.
  • When the drain valve is completely clogged, open several hot water faucets in the house. Turn off the power to the unit and leave the cold water inlet valve open so that cold water will dilute the hot water.

How to Unclog a Drain Valve

How serious the clog is will determine which solution works. This list starts with the easiest method first. We recommend starting at the top and working your way down until you find a fix that works. 

Whenever draining your water heater you should always turn the power and incoming water to off.​

1 - Give it Time

Many minor clogs will clear by themselves. The pressure from the water will give way and push the debris thru the open drain valve if given the opportunity.

  • Attach a garden hose to the drain valve and run the other end outside or to a drain.
  • Close all hot water faucets.
  • Open the drain valve.
  • Wait to see if the pressure from the water will push thru the debris. Give it a couple of hours.

2 - Stiff Wire

  • Begin with the drain valve closed and the hose disconnected from the drain valve.
  • Place a few towels below the drain valve or a pan to catch the water.
  • Open the drain valve and insert a stiff wire or a wire coat hanger into the opening into the tank.
  • Rotate the wire in a circular motion. This will help loosen the debris.
  • Water will begin to flow thru the valve if you were able to unclog the drain valve.
  • Continue inserting the wire until you have a good flow of water. Then turn the valve off and connect the hose.
  • It's common for the drain valve to clog several times during the process of draining the tank. Keep repeating until the tank is empty.

3 - Stomp the Hose

  • With the hose attached and the drain valve open, firmly stomp on the hose about 2 feet from the water heater.
  • A air bubble will be forced into the tank. This will often be enough to unclog the drain valve.
  • Be prepared to repeat the process as the sediment within the tank will most likely settle and clog the valve again.

4 - Reverse Flow

  • With the drain valve closed, connect one end of a washing machine hose to the drain valve and the other end to a garden hose.
  • Connect the other end of the garden hose to a threaded faucet, such as a washtub or outside faucet.
  • Turn on the water to the faucet and open the drain valve for about 10 to 15 seconds. 
  • As the water flows into the tank thru the valve, it should unclog the drain valve.
  • Turn off the water at the faucet, and close the drain valve.
  • Disconnect the hose from the faucet and open the drain valve.
  • The water should drain, however, if it doesn't, the drain valve is most likely defective or the clog is too severe.

5 - Replace the Drain Valve

If the you are unable to unclog the drain valve using the methods above, its time to replace the valve with a new one. Believe it or not, it is possible to do this with a full tank on water.

  • Wrap the treads of your new drain valve with Teflon tape. We recommend purchasing a brass drain valve.​
  • All of the hot water faucets in the house should be closed. A vacuum is created when the faucets are closed which keeps the water from pouring out.
  • Place towels and a pan under the drain valve.
  • Using an adjustable wrench unscrew the drain valve and quickly replace with your new valve.
  • During the process some water will pour from your tank. Try to be as quick as possible in switching valves and have towels available to rapidly clean-up the water.
  • Once the new valve is in place, connect a garden hose and drain the tank.

6 - Replace With a Ball Valve

Replacing your drain valve with a ball valve is not only resolving todays problem, but it is also a proactive method that will prevent your water heater from clogging in the future. Ball valves are much larger than the standard drain valve, and therefore are difficult to clog.

What you will need to purchase:

  • Wrap teflon tape on one end of the dielectric nipple. Then screw the wrapped end into the ball valve.
  • Wrap both ends of the other nipple. 3 of the 4 threaded ends of the nipples will be lined with Teflon tape. Determine which one to wrap by the ball valve handle. The handle should open away from the tank, wrap the nipple that the handle is moving away from.
  • All faucets within your home should be closed to prevent water from pouring out of the drain valve hole.
  • Place towels and a pan or bucket under the drain valve.
  • Use a wrench remove the drain valve and quickly replace with your new ball valve.
  • Some water will pour from the tank.
  • Connect a garden hose and open the ball valve to drain the tank.
  • It is a good practice to remove the handle on the ball valve when not needed. Most ball valves have long lever type handles that can accidentally be opened. If this happens your tank could drain without your knowledge, damaging the tank, creating water damage, possibly causing serious burns.

7 - Move Your Tank

Sometimes it just makes sense to move your tank outside and let it drain. If you are planning on replacing your water heater you may not want to go thru the hassle of changing your drain valve with a ball valve, and you don't really care about the condition of your tank after it is drained. 

In this scenario, moving your tank outside makes sense. But be careful, your tank will be extremely heavy, and we highly recommend cooling the water first. 

  • Disconnect the power source (gas line or electrical connection).
  • Disconnect the incoming and outgoing water lines.
  • Rock your water heater onto a hand truck and roll it outside.
  • Carefully turn the heater on it's side.
  • Allow the water to drain from the top of the tank.