It is fairly easily to drain a water heater, but it is a good idea to know what to expect before you begin.
- Be Prepared For A Leak - First, let me start off by telling you there is a chance that the drain valve will not shut back off all the way once it is turned on. Remember this drain valve has been sitting for six months to a year (or longer) and the older it gets the less likely it will shut off completely.
Be prepared to either put a cap over it or to replace the drain valve completely. If your water heater has a cheap plastic valve this is a good time to upgrade it.
- Quick Flush - Before you shut off the water hook a hose up to the drain valve and try and flush it a bit while the water pressure is on. To do this turn on the valve for a few seconds and then turn it back off.
This will blow any sediment stuck in the valve out with the pressure and make it much faster to drain. If there is quite a bit of sediment coming out you can repeat this a couple of times.
- Turn Off The Water Heater - Shut off the gas to your water heater. Now shut off the water either above the water heater or to the house. Make sure the pressure is off by turning on and checking the hot water fixtures in the house.
- Open Drain Valve - With your drain hose hooked up open the drain valve. This will not drain much at all until you release the vacuum in the tank. Remove one end of the hot flex line above the water heater and pull it to the side just a bit so the tank can get some air and the water will gush.
- Flush With Water - Once fully drained you can flush this with a few gallons at a time by turning the water on for few seconds at a time and then letting it drain out again. Leave the hot side flex line disconnected until your done flushing and then hook it back up before filling.
- Re-Fill Water Heater - Disconnect the hose and shut off the drain valve. Make sure to re-connect the flex line above the water heater and tightened it well. Now you can turn the water back on to the water heater. Open the hot side of a fixture in your house (the tub hot side is best).
Leave the fixture running until all of the air is out of the line and you are getting nothing but water out of the fixture then turn it off.
- Re-light Water Heater - Re-light the water heater and you should have hot water within an hour or so.
Check to see if your water heater drain shut off completely. If this did not you can put a cap over the hose thread of the outlet to stop the leak. The other way to stop the leak is to change the valve completely.