Draining a hot water heater can be either one of the easiest of projects to do yourself, or it can become a monster. The size, age, location, and type of water heater all factor into the difficulty of this job. Another consideration has to do with why you are draining this generally faithful device.If you are draining your hot water heater to perform service on it, you will often need to drain it completely to do your work. It can be harder to do a total drain than a partial. This is because it can clog up from sediment in the tank making it nearly impossible to get the water out of the last third or so of the tank. To exchange the tank or just remove it, you may only need to drain most of the water in order to move it with a hand truck.
To drain the tank, first survey the tank and the area where it is installed. The the tank should have a drain valve near the bottom. It should also have a water cutoff valve on the feeder line coming into the heater. You may need to locate the pop off valve near the top of the tank. If your heater is located in the basement near a drain with a nice slant in the floor, you may be able to just let the tank drain onto the concrete and run into the sewer drain. Most of the time, you will need a garden hose to attach to the drain valve on the unit.
Take time to figure out how to route the hose so that the tank will drain. Remember, water only really runs down hill. With a pump or syphon, you may be able to go over some obstacles on the way to a suitable place for draining the water. This will usually be outside. Turn the water off going into the water heater.
You will need to turn of all electricity coming into the unit before beginning to drain it. This will help avoid electrical shock, and it will keep you from destroying the electric heating elements inside the tank.Turn on a hot water faucet somewhere nearby. This will establish that the water inlet to the water heater is truly off and give a vent that is needed to let the water flow from the tank.
If all is well, you should now just need to open the valve at the bottom of the tank and let the water flow out through the hose to the drainage area.If no water comes out, make sure that the hose is not kinked or running uphill at some point. If the hose is going over a hump of some type, you will need to start a syphon with the hose to get the water running. The draining end of the hose will still need to be lower than the water in the tank. If you intend to drain the entire device, the hose will need to be lower than the valve it is attached to.
If you cannot get the hose to flow, turn off the drain valve and disconnect the hose. Now, open the drain valve just a little to see if water comes out. If it seems to flow in a reasonable amount, you will just need to reconnect the hose and work a little harder on getting it below the tank.
However, if when you open the valve nothing comes out, you will need to seek another source for the problem. Make sure that you have an open faucet to let air into the tank so it will drain. A way to test for an air inlet is to open the popoff valve at the top of the tank. If the water does not begin to flow, it means either the tank is clogged or the popoff valve is malfunctioning.
Get a wrench and disconnect one of the water pipes coming into the water heater. This is a sure way to get air flow. If the water runs, hook up the hose and drain the tank. If it does not flow, you have a problem.
You will need to get a stiff wire like a clothes hanger to push up into the tank through the drain valve. While doing this, you will encounter resistance. In older tanks, you can have up to half of the tank filled with sediment. The good news is that even if your tank is old, you should be able to loosen up enough of the sediment in a few minutes to let the water drain. It is possible to need to repeat this procedure a few times.
With electric water heaters, when you finally have it drained, pull the elements and see how deep the sediment is. If you were not planning a replacement, you may change your mind if the tank is half filled with sediment. This means that a forty gallon tank is probably only giving out twenty-five or so gallons of hot water.
In any event, let the water heater drain until no more water comes out. Close the valve and disconnect the hose. Do not turn on the electric until the water heater is either repaired or replaced depending on why it was being drained.