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How to Replace a Hot Water Heater

Updated on April 12, 2015
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Dan has been a homeowner for some 40 years, and has nearly always done his own repair and improvement tasks. He is a licensed electrician.

Replacing a hot water heater

Replacing an electric hot water heater is a simple task that most homeowners can easily perform. The addition of gas piping and vents can complicate the matter slightly, but even so is not difficult for the do it yourself type of person.

As always in performing such a task, the first step is removing all sources of supply and/or energy to the hot water tank. Turn off the water, either at the main valve feeding the house or at the hot water heater. Most heaters will have a valve on the cold water coming into the heater, and it is sufficient to turn off that valve. Turn off the power to the heater at the panel board. Turn off any gas supply. Safety cannot be emphasized enough; electric water heaters will normally be supplied with 240 volts and you certainly don't want gas flooding the house! Make sure that circuit breakers, fuses, water and gas valves are all turned off.

Be aware of the time involved; if the main water valve to the home is turned off the home will have no water for a couple of hours, or even more if plumbing needs to be redone. Make appropriate arrangements for at least a limited amount of water during the period.

Removal of the old water heater

Carefully remove any insulating blanket from around the hot water heater. If possible, save this insulation for later re-installation, but if torn and ruined you will need to purchase and install another insulating blanket.

Drain the hot water tank. There should be a valve at the bottom of the tank that will accept a water hose; attach a garden hose, run the hose outside and open the drain valve. Be aware that there will probably be rusty water coming out; don't position the hose as to stain a nice patio or other surface. Open both hot and cold water valves somewhere in the house. (Maintenance tip; once a year partially drain the water heater in this fashion to remove the inevitable sediment build up in the bottom of the tank for longer hot water heater life).

On the top of an electric water heater there will be a small steel plate where the wiring enters the tank. Remove the plate and gently pull the wires out. Using a non-contact voltage tester (if you don't have one this is a good time to buy one) test the wires for the presence of voltage. As noted, it will most likely be 240 volts, contact will result in injury or death. Make sure the circuit is off and there is no voltage present! Disconnect all wires from the old tank.

Remove the connections to any gas piping and test the pipe for gas leaking through the previously closed valve. It is a good idea to cover the exposed open gas pipe with a cloth or tape to prevent any trash from falling into the gas piping.

Using a pipe wrench or adjustable wrench, depending on the type of connection, remove the water piping from the top of the water tank. There may be a small amount of water lost from the piping as it is removed, so be prepared with a towel or rag to clean up small spills. If there is more than a cupful of water to come out the water is not turned off. Carefully bend the flexible water pipe up and out of the way just enough to remove the water tank. Inspect this flexible piping carefully; if it needs replacement now is the time to do it, and these short pieces are not expensive. If in doubt, replace them.

Using help if needed (water tanks are fairly heavy and quite bulky and awkward), remove the water heater and set aside for disposal.

Top of water heater, showing hot and cold water, relief water pipe and electrical plate
Top of water heater, showing hot and cold water, relief water pipe and electrical plate
Electrical plate removed for testing.  These wires are still energized!
Electrical plate removed for testing. These wires are still energized!
Drain valve on bottom of water heater.  One side cover plate for heating elements is also shown.
Drain valve on bottom of water heater. One side cover plate for heating elements is also shown.

Installation of the new hot water heater

Position the new hot water tank into the space where it will rest, and turn it to the proper orientation. Hopefully water, electric and gas piping outlets will be at least near the same locations, but the cover plates on the side of the tank cover the heating elements and these elements need to be accessible for future maintenance. If at all possible arrange the tank so that the cover plates can be reached.

Wrap any male pipe fittings with two or three wraps of teflon plumbers tape and re-install the water pipes. When applying the tape, start at about 1" from the end of the fitting and wrap the tape in a clockwise manner around the pipe, overlapping at least 1/2 of the tape width each time. The entire threaded area of the pipe should be covered with two layers of tape. If the tape is wrapped the wrong direction the action of screwing the pipe in will tend to dislodge it; if this happens simply remove the tape and re-wrap the other direction. Pipes should be tightened firmly with a wrench, but do not over-tighten copper threads; loose and leaking joints can be tightened but piping damaged from tightening too far will need replacement. Turn on the water and check for leakage at all joints. Wipe all joints dry and check after several minutes for any leaks - even a drop of water per minute is unacceptable.

Re-connect any gas piping, open the gas valve and check for gas leakage by putting soapy water over all pipe joints. Any bubbles at all indicate leakage that must be corrected; there must be absolutely no gas leakage at all.

The plate removed from the old water heater will have to be removed from the flexible conduit it is attached to; there is a large nut on the bottom of it for that purpose. The ground wire will also need to be removed, but pay attention to where it goes and how it is attached as the new water tank will have a very similar, but probably not identical, setup. Attach the new plate to the flex conduit and re-attach the ground (green or bare) wire. Using new wire nuts, attach the other two incoming wires to the two in the hot water tank. With a 240 volt supply it won't matter which wire goes to which (except for the green or bare ground wire) but small apartment tanks may operate on 120 volts and the white supply wire must attach to the white heater wire with the two black wires connecting to each other.

Make sure the tank is full of water by opening a hot water tap in the house and waiting until water comes out. Turn on the circuit breaker or fuse. Light any pilot lights according to the instructions with the new heater. It is a good idea to keep an eye on the water piping for a few days for any leaks; hot water and pressure could cause otherwise tight joints to leak slightly and they could need tightened.

Reinstall the insulating blanket. If the old water heater did not have such insulation it is strongly recommended that one be purchased and installed. The insulation blanket is one the easiest and cheapest ways to save energy in your home.

Congratulations! You have installed your own water heater, and it didn't cost an arm and a leg for a plumber to come and perform this simple task. If you have doubts of your ability to do this, I suggest you read this article about doing your own home repairs.

Electrical cover plate.  Note the bare ground wire fastened to the top of the plate.
Electrical cover plate. Note the bare ground wire fastened to the top of the plate.
Electrical plate removed, showing the conduit connection nut.
Electrical plate removed, showing the conduit connection nut.


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    • snakeslane profile image

      snakeslane 5 years ago from Canada

      Good information here, really helpful, thanks.

    • wilderness profile image

      Dan Harmon 5 years ago from Boise, Idaho

      Glad it was useful - hope your project goes well. Thanks for the comment.

    • snakeslane profile image

      snakeslane 5 years ago from Canada

      Well actually I am just going to call a plumber and let him deal with it, but I did shut the power off at the breaker and turned off the tap so the loud hissing noise stopped. Now to do dishes I have a big pot heating on the stove, just like the old days, too funny.

    • wilderness profile image

      Dan Harmon 5 years ago from Boise, Idaho

      If there is a hissing noise, then definitely it is time to take some steps, and those are the proper ones if the tap you refer to is at the top of the hot water tank.

      Yes, I've heated water on the stove as well. Just for a couple of days when the valve at the bottom of the tank suddenly broke off and shot across the room at 2AM. Along with LOTS of water! It took a couple of days to shop around, find a new tank and install it.

    • profile image

      Dag47 2 years ago

      Can 1" supply lines be used in place of 3/4 " supply lines falcon flex?

    • wilderness profile image

      Dan Harmon 2 years ago from Boise, Idaho

      Sure. You will just need to reduce it down to match the tank, that's all.

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