A water heater that appears to be in decent condition without a lot of corrosion at the connections or, leaking is an ideal candidate for rebuilding. Changing out the thermostats and elements will restore the ability to produce a full tank of hot water for your use. Changing out a T&P valve will ensure that the water heater operates safely without building up dangerous temperatures and pressures within the water heater. Changing out the anode rod will help prevent the steel tank from corroding and leaking which would make you have to replace the water heater. If you want, you can opt to troubleshoot the water heater and replace only the components that have actually failed or, have worn or, been consumed. Generally when I’m rebuilding a water heater i replace it all rather than risk returning to replace something later. Of course you are dealing with an old tank still that appears to be in good shape but there is always a possibility the tank could start leaking tomorrow.

How To Drain The Water Heater

The first step when rebuilding the water heater is to empty the tank. Draining the tank is only necessary if you are changing the elements. The T&P valve and anode rod are located at or, near the top of the tank so a partial draining is all that is needed when working on those items. The first thing you need to do in order to drain the tank is to shut off the electrical power to the water heater. If you can run a garden hose from the drain at the base of the tank to a point that is lower than the water heater drain to drain the water you will not need a pump. Even if the hose goes higher than water heater drain as long as the hose end where the water comes out is lower the water heater will drain by siphoning. If the water heater is lower than the drainage point like in a basement installation you will need a pump that hooks up using garden hose connections to drain the water heater. I start the draining process by opening the drain valve allowing water to flow out using the water pressure in the water heater. Once the flow through the hose has been established I shut off the water feeding the water heater and open a hot faucet allowing air to enter the tank so it will continue to drain. Once the tank has drained down below the T&P valve connection I usually prop the T&P open as well. Once the tank has emptied and water stops coming out of the drain you are ready to rebuild the tank.

How To Change Thermostats

The thermostats are located under the two access panels on the side of the water heater. Always ensure that electrical power has been shut off to the water heater before removing the access panels. Electric water heaters in a home are typically powered with 240-volts which poses an electrocution hazard if the panel is removed while power is still applied to the water heater.

Using a screwdriver take the wires off the old upper thermostat keeping track of which ones supply the power from the power panel, supply power from the upper thermostat to the upper element, and supply power to the lower thermostat and element. Once the wires have been disconnected lift the tabs holding the thermostat in place and slide the thermostat up and out of the water heater. Slide the new thermostat into place under the locking tabs. The new thermostat may have slight variations in the terminals used so follow the instructions included with the new thermostat for wire placement on the new thermostat. Make sure that you tighten the terminal screws, loose connections can generate heat and cause the thermostat to burn out.

Once the upper thermostat has been replaced, move down to the lower thermostat and replace that as well. The lower thermostat is a lot easier with only two connections to make up. Make sure that both thermostats maintain physical contact with the tank because the temperature is detected by the thermostat conducting heat from physical contact with the tank. If the metal plate on the back of the thermostat is not touching the metal tank the water will not be heated to the correct temperature and dangerous overheating of the water can occur. Make sure the thermostat is set to a safe temperature in accordance with the plumbing code used in your area.

How To Change The Elements

The elements are also located under the same access panel as the thermostats just below the thermostats. They have two screw terminals for the power connections and in most cases the elements are a 1½” socket size hex head that screws into the tank. Most water heaters use 4500-watt elements and you should get replacement elements that match the ones your water heater uses. There are some water heaters that use lower wattage elements and some places sell 5000-watt elements, but you should not change the element wattage when replacing them. The circuit breaker and wires may not be able to handle the larger power requirements on higher wattage elements and lower power elements will reduce the recovery rate of your water heater.

One thing that you should consider is upgrading the quality of the element you install, at least on the lower element that typically does most of the work and can become buried in mineral sediment causing it to burn out. Elements made out of Incoloy which resists corrosion, are available, as well as low-watt density or, ultra low-watt density elements, which run cooler resisting burnout, yet still deliver the same amount of heat into the water. The lower wattage density elements still have the same wattage but the elements are longer and run cooler resisting burnout. Some ultra low-watt density element manufacturers actually claim their elements will not burn out from sediment buildup and can even be dry fired without burning out.

An inexpensive stamped steel socket is typically sold for replacing water heater elements but I have found they are difficult to use and often slip of the element. I prefer to use a 1½” six point socket and a breaker bar for replacing elements. Disconnect the wires from the element, and then use the socket to unscrew the element from the water heater, and pull it out of the hole. While the lower element is removed you should go in through the hole to remove the sediment from the bottom of the tank. I usually use my wet dry vac and a piece of 1” tubing on the end of the hose to get inside the tank, and get the sediment out. Take the new element and insert it into the tank then get the threads started and tighten with the socket. The weight of the element makes starting the threads difficult, you will have to press the element firmly into the hole to keep it straight when starting the threads. Once the element is tightened connect the wires to the screws and replace the plastic safety cover that goes over the thermostat and elements. Then replace the access covers and secure them.

How To Change The T&P Valve

When replacing the T&P valve on your water heater you should be certain to get a properly sized T&P valve for your water heater. In most residential electric water heaters a Watts 100XL T&P valve will suffice but you need to make sure the T&P you install is adequate. The drain line from the T&P valve will have to be unscrewed from the T&P valve so the T&P can be unscrewed from the tank. In some cases the drain line will have to be cut then rejoined after the T&P is replaced. If the T&P has 2 flat surfaces for a wrench then a large adjustable wrench can be used for removal. If it doesn’t have 2 flat surfaces then use a large pipe wrench for removal. Make sure if the T&P valve is located on the top of the water heater that you have the water heater braced to prevent it from spinning and damaging the pipe and wire connections. Put Teflon tape on the threads then apply Teflon paste over the tape to ensure a leak free connection and thread it into the water heater and tighten making sure the discharge lines up properly and reconnect the discharge pipe.

How to Change The Anode Rod

The anode rod is a sacrificial metal that is consumed typically in about 4 years although it varies with differing water conditions. The anode prevents the steel tank from corroding and replacing the anode when needed can greatly extend the life of your water heater. The anodes supplied as original equipment in water heaters are magnesium although certain water conditions may cause sulfur odors in which case an aluminum or, aluminum-zinc-tin anode should be used. Where there are clearance problems on top of the water heater a segmented or, flexible anode rod can be used. The anode will typically be attached to a plug, which screws into the top of the tank or attached to the bottom of the outlet nipple. On the plug type anode I use a cordless impact wrench and socket to remove and install them. If you use a socket and breaker bar or, are removing the hot outlet nipple using a pipe wrench make sure you brace the water heater to prevent it from spinning and damaging the pipes and electrical connection. Of course if the anode is on the hot outlet the pipe will have to be cut and rejoined as well. When putting the anode back in wrap Teflon tape on the threads and apply Teflon paste over the tape then thread the anode in and tighten.

Refilling The Water Heater

After rebuilding a water heater I close the hot faucet and turn on the water while the tank is full of air allowing the tank to pressurize while the drain is still open allowing the incoming water to blast against the bottom washing any remaining sediment out of the tank. Once the draining water is clear I close the drain and reopen the hot faucet to allow the air out and the tank to fill. Once the water is coming out of the faucet with no air I close the faucet and turn the power back on to start the tank heating.

The thermal expansion tanks used on water heaters should be listed as “Potable Water Expansion Tanks” which means they are constructed from materials that are safe to use on drinking water systems. Expansion tanks are also used on hot water boilers but the water in those systems are never consumed so the materials used are different. Make sure the right type of expansion tank is used on your potable water system. The expansion tank should be connected on the inlet side of the water heater and connected by a tee between the inlet to the water heater and the shut off valve on the inlet of the water heater. There should be no valve between the water heater and the expansion tank, which would defeat the protection provided by the expansion tank. The water in the tank will add considerable weight to the expansion tank and it should be adequately supported to avoid placing stress on the pipes. The tank may have a longer line plumbed to it allowing the tank to be remotely mounted. it does not have to be directly on top of the water heater.

Potable Water Thermal Expansion Tanks are made by a few different companies, Watts with their model PLT-5, PLT-12, PLT-20, and PLT-35 tanks used in residential and light commercial, and Amtrol with their Therm-X-Trol model ST-5, ST-8, ST-12, and ST-25V tanks also used in residential and light commercial are very popular. Larger commercial water heating systems would require using an ASME Rated expansion tank. The tanks are made of drawn steel that has a rubber bladder dividing the tank into two sections. On one side there is a threaded connection that allows water to enter the tank. On the other side there is an air valve similar to the one on a tire through which the air pressure of the pre-charge on the air side of the bladder can be adjusted and checked. The pre-charge should match the typical pressure on your water supply system. The air is able to compress which allows the expanding water to enter the expansion tank with only a slight increase in system pressure preventing the water heater tank from experiencing pressure cycles and providing a substantial increase of the service life expectancy of your water heater.

To get ready to replace the T&P Valve you will need to shut off the water supply to the water heater and shut off whatever is used to heat the water so it does not try to reheat while you are working. You will also have to drain the water heater tank down so that the water level is at least below the level of the T&P Valve. The next step is to disconnect the discharge tube from the T&P Valve. The discharge tube is threaded into the valve and it should easily come out using the wrench. Again if the tube is run in a manner where it cannot swing to unthread the tube will have to be cut. After disconnecting the tube, the T&P Valve is also threaded into the water heater tank. It should have a flat surface where the wrench can fit to turn the valve. Some brands of T&P Valves have only one flat surface but not to worry the adjustable wrench still will work. Turn the T&P Valve counterclockwise to remove it.

Once the T&P has been removed the new one needs to be prepped for installation. In most cases a residential water heater can use a T&P valve like the Watts Model # 100XL which has a 150 PSI. 210 Degrees F, 105,000 BTU/hr rating. However, there are high-output water heaters which require a larger valve. You need to make sure that the protection afforded is adequate for the water heater you are installing it on. If the level of protection is not adequate on the valve you are installing you risk danger of the water heater exploding. Once you are certain that the T&P Valve has the correct ratings to do the job of protecting your water heater you need to put Teflon tape on the male threads of the T&P Valve. Wrap the Teflon tape in a manner where it will not be trying to come undone when you thread the T&P Valve into the water heater tank. Then once the Teflon tape is wrapped apply Teflon Pipe Dope over the Teflon tape. This is just a preference of mine and is kind of like wearing a belt and suspenders approach. With this I have found that it offers a much greater chance of a threaded connection being leak free. It works for me!

Once the new T&P Valve has been taped and doped you can the screw it into the tank. Turn it clockwise to screw it in. As it tightens up you have to gauge where the outlet is going to land so that it lines up properly with the discharge pipe. You have to be careful where you stop turning it so you get a leak free connection and you also have to stop where it lines up properly with the discharge pipe. To loose and it will leak, and too tight you will be left with the valve facing the wrong direction without being able to continue turning all the way around to the correct position. You cannot just loosen it backwards into the right position without getting a leak. If you go too far you will need to take it back out and retape and dope the threads. Many times I get it close to the right position then put in the drain tube and turn it the rest of the way into perfect alignment.

Once the T&P valve has been threaded into position you are ready to install the drain tube. The drain tube has some specific requirements for where it drains to that may have changed since the water heater was initially installed. It is in your best interest to upgrade to the code used in your area. Either research the code and amendments used in your area or, just ask the plumbing inspector what the requirements are.

Where I live the code states:

1.) The outlet of the T&P Valve cannot be directly connected to the drainage system. There must be an air gap where it connects to the drain system so that contaminants from the drain cannot be sucked back into the potable water if the water supply were to have a negative pressure.

2.) The T&P valve discharge tube will be full size which means if the outlet on the T&P Valve is ¾” the tube and all connectors used will be 3/4” I.D. The outlet cannot be restricted.

3.) The discharge from the tube must discharge to a safe place such as the floor, outside the building, or an indirect waste receptor.

4.) The discharge tube cannot have any trapped sections meaning the tube must maintain a downward pitch so that it drains completely dry.

5.) The discharge tube needs to have a visible air gap or air gap fitting located in the same room as the water heater.

6.) The outlet end of the discharge tube cannot be threaded and the discharge tube cannot have a valve between the T&P Valve and the disposal point. What this means is there cannot be any easy means of capping the discharge of the T&P Valve. If the valve opens it needs to flow freely to prevent an explosion of the water heater.

7.) The T&P Valve discharge tube needs to be installed in a manner that does not cause personal injury to occupants in the immediate area or, structural damage to the building. In other words hot water blasting out of the discharge tube cannot go to a place where it will hit people, and the flooding from it cannot damage the building.

I would anticipate the code in your area having similar requirements. Again check to see what the code requirements are where you live. There is not one code that covers the whole United States or even most states. Codes can even have amendments at the local level.

Once the discharge tube has been installed you can turn the water to the heater back on and run hot faucets to bleed the air out of the tank and allow it to refill. If the flow slows at any of the faucets remove the aerator from the faucet and clean out any debris. Check the connection where the T&P Valve threaded into the water heater for leaks. Then turn back on whatever is used to heat the water and once hot again recheck for leaks at the connection of the T&P Valve and the water heater.

If the water temperature exceeds the boiling temperature of water the water heater could have a steam explosion. So the valve is set to open at 210 Degrees F and if the water temperature in the water heater were to cause T&P Valve to open there would be a fairly large release of water until the water in the water heater became cooled enough by the incoming water to allow the T&P Valve to reset. This would be an instance where the T&P Valve was doing its job and replacement is not warranted. Instead you should look at a failed thermostat that is not turning off at the set temperature, the upper thermostat should also have had the red reset button pop out as the reset button is a temperature activated device. Another problem could be an element that is shorted to ground. The 240 Volt supply is only switched on one side

so 120 Volts from the unswitched side could continue to flow even with the thermostat shut off through at least part of the element to ground and cause heating not controlled by the thermostat. If you were to replace the T&P Valve in this circumstance the new one would do the same thing the problem needs to be diagnosed and repaired.

Water releases caused by pressure can be a little harder to diagnose and cure. They may be caused by the supply line pressure being too high or, thermal expansion within a closed system. In any case a pressure gauge with a “lazy hand” that screws onto a hose bibb will be useful in diagnosing pressure problems. The “lazy hand” is a hand which is pushed to the highest pressure recorded by the gauge needle and does not lower until you reset it. The first thing to check is the system pressure. By most codes if the pressure goes above 80 PSI. a pressure reducing valve and thermal expansion tank should be on the system.

To test the system pressure make sure the water heater is not heating the water in the tank. Run a small amount of cold water to release the build up of pressure due to thermal expansion or, a failed pressure reducing valve, screw the valve on a hose bibb and turn on the hose bibb. The reading you get is the system pressure. If it is greater than 80 PSI. a pressure reducing valve and thermal expansion tank should be installed. If there is already a pressure reducing valve installed it has failed and requires replacement. If it starts out less than 80 PSI. and slowly creeps higher then you probably have a pressure reducing valve that is leaking and allowing the pressure to increase past its set point and it should be replaced. If the supplied pressure approaches 150 PSI. the T&P will open and flow water as long as the pressure it too high. If you have at this point checked the temperature and pressure and both are within the normal parameters of the T&P Valve yet the valve is still open and flowing at this time replace the T&P Valve. Once this test is resolved you should proceed.

Next we have  to test for thermal expansion. Run a lot of hot water. Have someone take shower or take a bath. Watch the gauge as the water in the water heater is heated without running any water in the house and see what happens. If the pressure creeps up while the water is heating it is a sign that the water supply is a closed system and thermal expansion is causing the pressure rise. Generally the discharge of water from thermal expansion is a small amount like a coffee cup or, two. Any rise or, discharge from thermal expansion would indicate a thermal expansion tank should be installed. The thing you are looking at is the water heater is a pressure vessel. Cycles of pressure is taken into consideration of the design but it’s a lot like the nine lives of a cat. You use them and you loose them, there are just so many pressure cycles built into the tank before it fails and a thermal expansion tank absorbs the pressure instead of the water heater. Once this test is resolved you can proceed or, proceed with out using any hot water after the water heater has finished reheating and you have run cold water to eliminate any stored thermal expansion.

The next step is to watch the supplied pressure over a period of time. Leave the gauge on at least overnight without running hot water or, if you have resolved that thermal expansion is not a factor you can use hot water. Frequently at night water companies run higher pressures as they fill storage tanks to be ready to meet the water supply demands the next day. This is where the lazy hand is required so it can record any pressure spikes over an extended period of time. Again, if it goes over 80 PSI. a pressure reducing valve and thermal expansion tank should be installed. Ideally you would run this test for a 24 hour period.

If you have run through these diagnostic tests and determined that the leaking T&P Valve is not leaking for one of the above reasons replace it. Just a side note the actual numbers at which the valve is rated to open at has a fairly wide tolerance so it may open slightly before the rated temperature or, pressure. If the pressure is over 80 PSI. or, over the set temperature there is a problem that requires resolution.

There are many times when the potable water system in a home can become a “Closed System” meaning water can only flow into the home and not out. This is a desirable thing as it can guard against contaminants entering the water supply in a backflow situation. Whether it is a check valve in the meter or, elsewhere, or, a pressure reducing valve without a bypass your system can become a closed system. When a system is closed dangerous pressures can build in the system when the water heater reheats due to thermal expansion or, a malfunctioning water heater that heats the water too hot. The maximum working pressure in a water heater is 150 PSI this is established by testing and design. In all reality the actual burst pressure is much higher as the working pressure is a derated safe figure and the burst pressure is probably in the 300 PSI range.

The T&P valve has 2 functions. “T” is for temperature, and “P” is for pressure. The pressure setting of the valve is usually 150 PSI and the temperature is 210 Degrees F. The pressure exceeding 150 PSI will cause the valve to open releasing the excess pressure maintaining a safe pressure below the 150 PSI working pressure. If the temperature exceeds 210 Degrees F the danger is far greater because the high pressure in the system will prevent the water from turning to steam so you can have an entire water heater full of water hot enough to convert to steam but not converting due to the system pressure. When the temperature exceeds 210 Degrees F the valve will open and flow water until the temperature drops. If the water heater were to burst when the water is overheated above boiling, the entire contents of the water heater will instantly convert to steam. This steam will expand 1,600 times its original volume of water. This is when the launch occurs.

The T&P Valve is a relatively inexpensive device that is threaded into either the top of the water heater or, the side of the water heater near the top. There should be a tube connected to the valve which may run down towards the floor under the older codes or, under new codes it may run to a place where it can drain without causing water damage. This tube must be allowed to drain dry by gravity. If water was not able to drain out dry the metal parts could corrode and cause the valve to fail. The water in the pipe could also freeze in colder climates causing an ice plug to form in the pipe. This pipe must never be plugged or the T&P valve will become ineffective greatly increasing the danger level.

The test is simple. On the T&P Valve there is a small handle that lifts a pin in the center of the valve. Before testing make sure you are in a safe position where you will not be struck by the hot water discharge, and that you know how to shut off the water supply to the water heater. You don’t have to turn it off but you need to know how to do it as the valve when tested may not reseat properly causing water to leak. If this occurs you will need to be able to shut off the water until the valve can be replaced. All you need to do for the test is lift the handle so the valve opens then release it so it closes. If the valve is frozen so it does not open or, does not close it should be replaced ASAP. Sometimes the valve may not set properly after testing. Try opening it and allowing it to slam shut several times. If this works the valve is okay. If it doesn’t it should be replaced. This test does not ruin a valve. If the valve fails the test it was already bad and was not offering the protection you need. Regular testing may actually increase the life of the valve. Test the valve a minimum of once a year.

Water heater anode rods come in several types, a solid rod that extends from a plug, a solid rod that extends from the outlet nipple, and a segmented or, linked rod for when there is a lack of overhead clearance. The segmented rod is available with either the plug or, outlet nipple type. You will need to determine whether your water heater takes a plug or, outlet nipple type anode. You will also need to determine if you have enough overhead clearance to get the rod in and out of the top of the water heater. The old one will bend easily but, the new one will not and needs to go in straight. If there is not enough overhead clearance you need to use a segmented anode.

This is also a good time to test the T&P Valve by lifting the handle and making sure that it discharges. Release the handle allowing it to snap closed. If the T&P valve does not open with the lever, or fails to close and leaks after testing it must be replaced. This is a critical safety device that can prevent the water heater from exploding.

You will also need to determine what kind of metal the anode needs to be made of. The most commonly available anode is magnesium, in fact that is the stock anode that comes in water heaters. Some water conditions may cause sulfur odor in the water when a magnesium anode is used. If this is the case an aluminum anode or, aluminum/zinc/tin anode rod should be used and the water heater disinfected as the odor is actually caused by a sulfur reducing bacteria.

While changing the anode does not require a complete drain down of the water heater and can be done by just lowering the water level in the tank slightly below the top I will describe how to do the work in conjunction with flushing the water heater.

1. Turn off the Water Heater. On an electric water heater, turn the water heater circuit breaker off. On a gas water heater, turn the gas valve to the off position.
2. Connect a hose to the drain valve on the heater and run to a drain or, outside. It must be lower than the water heater or, a transfer pump will be needed. Turn on the drain and allow the pressure to establish a flow.
3. Shut the cold water off to the water heater.
4. Open a hot water faucet to allow air to enter or, the tank will not drain.
5. Allow the tank to completely drain.
6. Close the hot faucet.
7. Turn back on the cold water into the water heater.
8. Allow the water to run through the water heater and out of the drain valve.  Do this for approximately five (5) or ten (10) minutes until there is no longer and debris coming out of the hose.
9. Shut off the cold water and close the drain valve.
10. Reopen the hot faucet and the cold supply valve to the water heater partially refill the water heater about ¾ full to get some weight in it.
11. Close the cold supply valve to the water heater.

You are now ready to replace the anode rod.

If your water heater has the anode on the outlet, the pipe will need a way it can be broken apart to unscrew the outlet nipple. You will also need a means of reconnecting the pipe when finished. There are many possibilities ranging from installing a union, using a repair coupling, or, a Sharkbite coupling. If you have any questions on what to do I would suggest asking at an online plumbing forum such as Terry Love’s Plumbing Forums. Unscrew the outlet nipple using a pipe wrench, and remove the old anode. You will need someone to help keeping the water heater from spinning while taking out the outlet nipple. Once it is completely loosened pull the old anode rod out. Take the new anode and apply Teflon tape to the threads of the nipple then apply Teflon paste on top of the threads. Lower the new anode into the water heater tank and thread the nipple into the water heater. Remember to have someone help you when tightening or, loosening the nipple to prevent the water heater from spinning and causing damage to the pipes.

If the anode is the plug type I use a cordless 1/2″ drive impact wrench and socket. This works very well and is the same type of equipment the factory uses for installing them. With the impact wrench there is no danger of spinning occurring. If you do not have an impact wrench, a breaker bar and socket can be used to unscrew the anode plug. However, help will be needed to prevent the water heater from spinning and pipe damage.  Once the plug is loose lift the old anode rod out of the water heater. Ready the new anode for installation by wrapping the threads with Teflon tape and apply Teflon paste over the threads. Lower the anode rod into the tank, and tighten the plug using the opposite manner from the way it was removed. Again if a breaker bar and socket is used get a helper to prevent the tank from spinning.

1. Reopen the cold water valve to the water heater and allow the tank to refill, keeping the hot water faucet open.
2. When water comes out of the faucet, the tank is full. Close the faucet. (Note: Sometimes when work of this nature is performed the aerator on the faucet may clog with debris. If the flow lowers or stops unscrew the aerator clean the debris and reinstall.)
3. Check your work for leaks.
4. Turn the water heater back on.
5. Once hot recheck for leaks.

While no water heater will last forever regular flushing and making sure the anode is protecting the water heater you should in most cases extend the life of your water heater.