Water heater draining at intervals, between 6-12 months, is recommended by most water heater maintenance guides. This is advised so as to help take out any buildup or sediments collected at the water heater tank bottom.
While draining a water heater is fairly easy, you should have an idea of what to expect as follows.
You need to prepare yourself for a leak. It's possible that after opening the drain valve to the tank it won't close fully again. Keep in mind that this particular drain valve has been sitting idly for six to twelve months (or even longer), and over time it gets less and less likely to close completely again.
Do a quick flush.
Before shutting the water off, hook up the drain valve with a garden hose and try to flush the tank of the water heater for a while as the water pressure is on. In order to do this, leave the drain valve open for some seconds and then close it again. Any leftover sediment in the valve will be blown out by the pressure, helping to boost the drain speed of the tank. If a minor amount of sediment is found, repeat the process a few more times.
Turn the water heater off.
If yours is an electric heater, shut off the power; otherwise, shut off the gas supply. Now shut the water off by using either the cold water valve located above the water heater unit or the home's main water supply valve. Ensure the pressure is relieved by turning the water faucets on to check for hot water.
Open the drain valve.
Open the drain valve while the drain hose remains attached. Until the vacuum in the tank is released, it will not drain so much. In order to do this, disconnect one end of the hot water pipe located above the water heater unit and place it closely aside. Air will then be allowed into the tank, and in turn allow water to flow through the drain.
Use water to flush the tank.
After draining the tank fully, you can use a few gallons at a time to flush it. Do this by turning the water on for a few seconds and draining it out again. Only after flushing is done, reconnect the hot water pipe and refill the water heater tank.
Refill the tank of the water heater.
Detach the drain hose and shut the drain valve. Ensure the hot water pipe earlier disconnected in reconnected and tightened properly. You can now turn on the water supply to the water heater unit. Leave a fixture in your home open (preferably the bathtub) to the hot side. Allow the fixture to run until the lines are completely free from air and nothing but water comes out of the fixture. At this point, you can turn the water back off.
Repower the water heater.
Turn on the power to the water heater, if electric; or, relight the pilot of the water heater unit, if gas. Your hot water should be ready in about an hour.
Inspect the drain valve.
Confirm if the drain of your water heater closed fully by checking for leaks at the spout. If it failed to close fully, you can place a cap on the outlet hose thread in order to stop the leak. Otherwise, you can have the valve replaced.