Whirlpool Water Heater Drain Valve Replacement. Also if your drain valve is made . Switch off the power supply. Removing an old, leaking drain valve. If there is water leaking from the threads or out of the drain valve body, then the valve should be replaced. Turn the cold water supply valve off. In this episode of repair and replace vance explains how to effectively remove the stem from a broken plastic drain valve in a water heater. Just make sure to use a new valve that matches the old one.