How to Replace a Hot Water Heater Drain Valve
All hot water heaters are equipped with a drain valve located near the bottom of the tank. Hot water heaters should be flushed at least annually to remove sediment, but if you are trying to flush sediment out and the drain valve has clogged it may need to be removed to clean out the sediment. Old valves may crack and leak, especially plastic ones that are found on many models. Leaking or malfunctioning drain valves should be replaced immediately to prevent potential property damage.
A better solution is to install a full-port brass ball valve that can be opened quickly to flush the sediment out.
If you do opt to install a ball valve, make sure that the valve is made for hot water heaters, is dielectric, or install a dielectric nipple between the hot water heater and the brass ball valve.
Hot water heater drain valve
Plastic Hot Water Heater Drain Valves
Plastic drain valves will eventually leak due to the materials they are made. Plastic drain valves are used because they are inexpensive and will not cause galvanic corrosion.
Older style plastic drain valve
Components of plastic drain valve
The rubber in the seals harden all rubber will eventually dry out and harden weakening the seal and cause the valve to drip.
Tools and Materials
Garden hose and Bucket
Pipe sealer or Teflon tape
A standard drain valve for a residential hot water heater is 3/4 inch.
1. For electric water heaters, turn the power off at the circuit breaker. For gas water heaters turn the control valve to PILOT. Since the water inside the tank is hot, open the hot water faucet in a sink or tub until the water runs cold. Shut off the faucet.
2. Shut off the hot and cold water supply valves at the top of the water heater. You can attempt to replace the drain valve without draining the tank by creating a vacuum inside. Some water will come out when the valve is removed. If the water heater is older and you are replacing a plastic drain valve, there is a good chance that it may break off and you will not be able to install the new valve. It is recommended that you drain the tank completely.
Connect a garden hose to the drain valve and drain the hot water heater. Open the temperature Pressure Relief valve or open the hot water supply valve at the top of the heater and a hot water faucet in the house.
3. Prepare the new drain valve by wrapping the threads with Teflon tape or applying pipe sealer.
4. Use an adjustable wrench or pliers to remove the valve. You may want to look inside the tank with a flashlight to see if there is any sediment inside the tank.
5. Install the new drain valve and dielectric nipple if necessary. If you are installing a ball valve, make sure that the handle is open (parallel to the valve body) so that there is enough room to operate the valve. You may also want to install a 90-degree elbow after the dielectric nipple so that the valve does not stick out from the tank.
6. Open a hot water faucet at any sink or tub in the house. Then turn on the cold water shut-off valve that was turned off earlier. Allow the water heater to fill. Close the temperature and pressure relief valve and the faucet when the water is running at a steady stream.
7. Check the new drain valve to make sure it is not leaking. Turn on the gas supply or power to the water heater.
Removing a Broken Drain Valve
Whether the drain valve is plastic or metal, removing a drain valve that has broken off inside the tank will require the stem to be removed before the new valve is installed.
Use a hacksaw blade to cut along the length of the stem in at least 3 places. Then with a flat screwdriver and a hammer, carefully tap the edge of the stem until it pops out. Remove the remaining pieces with a pair of needle-nose pliers.
Cutting the threads of a broken plastic drain valve