Water Heater Repair: Troubleshoot and Replace Thermostats and Elements
Learning to Troubleshoot and Repair Hot Water Elements and Thermostats
Sooner or later every hot water tank will fail and it is time to replace it or troubleshoot and repair it. Unless there is physical damage resulting in leaks the problem will be in either the thermostat or heating elements; these are simple appliances and there just isn't very much that can go wrong.
Nearly all residential hot water heaters have two thermostats and two heating elements. In normal, low water usage conditions, the lower element is the one doing the work. It is only under high water requirements that the entire tank will cool down; the lower element will then shut off and the upper element takes over the load. This heats the upper portion first and produces a quicker recover time.
Troubleshooting these parts is not difficult, but does require working around live, high voltage wires and connections. If you are not comfortable doing this, it is probably best to simply replace the entire unit or call a plumber. Or simply change parts without troubleshooting them; elements and thermostats are inexpensive enough that all four pieces could be changed and still save over half the cost of a new water heater.
Troubleshooting the Thermostats and Heating Elements
The first step in troubleshooting a hot water heater is to gain access to the areas to be tested. As you will need to get your fingers into the area occupied by hot electricity; turn off the power at the breaker panel. It will be a two pole breaker; that is, two breakers will be connected by a bar and will turn off together.
Once the breakers are turned off, remove the two access panel covers shown in the photo to the right. You will find insulation inside, but it is cut to the size of the opening; pull this out and set aside for later re-installation. Now exposed is the thermostat and heating element, covered by a simple plastic cover. The top thermostat has a built-in circuit breaker button accessible through the plastic cover; push it and make sure it wasn't tripped. If you feel a "snap" or think that it had tripped you might turn on the power again and give it time to heat the water - this could have been the whole problem, although the question of why it tripped at all has not been addressed yet. If you continue to troubleshoot it would be best at this point to check that the power is indeed shut off by using a non-contact voltage detector if one is available. The only wires that you are assured of as being hot are the pair at the top; wave the detector in that area to see if it lights up or beeps.
Whether you have checked voltage or not, assume the unit is still powered. Carefully remove the plastic cover; they will usually either simply snap out or will need to be worked out from under a hold down support. Do not stick your fingers any further into the opening than is absolutely necessary! With the cover out of the way check for voltage at the top two screws by setting a voltmeter to a voltage setting of at least 240 volts and putting one test lead to each of the top two screws. If voltage is detected the power is not turned off yet; turn it off and re-check. Only when the power is turned off should you continue.
Testing the Heating Elements
See the photo for location of the heating elements. These are vaguely round, with a large hex nut behind them. There is one behind each access door, and each one will have two wires going to it. Remove one of the wires from the heating element and test for resistance (ohms) by setting the meter to the lowest resistance setting available. With a test lead on each wire terminal of one of the elements, read the resistance; it should be around 12 ohms for a common 4500 watt heating element. If the meter shows OL (overload) or infinite, the element is broken and needs replaced. If the reading is very low, perhaps just an ohm or two, the element will probably not last much longer and you can expect to replace it at any time.
Next test with one lead on the metal tank itself and the other on one of the terminal screws. The reading should be infinite, or OL. Repeat for the other terminal screw. If either of these readings are anything but infinite the element needs replacement.
If either element needs replacement make sure you purchase one of the correct wattage and voltage.
Testing the Thermostats
Troubleshooting thermostats in a hot water heater requires that the power be turned back on. This will supply 240 volts to the heater; if you touch any bare wires or terminals you will receive a severe shock that can be deadly. Extreme caution is required!
Test voltage at both heating elements by putting a test lead to each wire terminal, one element at a time. There should be no voltage if the water in the tank is hot; if it is not allow some time to heat up and re-check. If one or both elements are "hot" even with hot water in the tank one or both thermostats need replacement, but it would be unusual to fail in the "on" position and the result would be water escaping from the safety valve at the top of the tank. More likely the water just isn't hot yet; give it some time. Once both elements are "off", proceed with the next step.
With hot water in the tank check voltage at the lower thermostat by putting a test lead on each of the two screws on that thermostat. It should read 240 volts; if it does not the upper thermostat is bad and needs replaced.
Turn on the hot water in a sink or tub and check the lower heating element every couple of minutes. As hot water is drained from the tank it is replaced with cold water, and the tank will eventually become cold enough to turn on the lower heating element by applying voltage to that element. If the lower element never comes on the lower thermostat is bad and needs replaced.
Continue to run hot water in the sink. As the water in the tank continues to cool, it will reach a point when the lower thermostat shuts off and the upper thermostat turns the upper heater on. Continue to check the upper heating element for voltage - it may take quite a while and the water may have to quite cold, but it should come on eventually. If the upper element never comes on even though the water running in the sink is quite cold the upper thermostat is bad and needs replacement.
Opening the Hot Water Tank
Replacing the Thermostats and Heating Elements
Whether it is elements or thermostat that needs replacing, turn the power off and check that it is indeed off.
Replacing the Heating Element
The tank needs to be drained; attach an ordinary garden hose to the drain valve at the bottom of the tank, lead the hose outside and open the drain valve. The tank probably has sediment it, wait until clear water is coming from the hose and turn off the water supply valve to the tank. Water will not drain this way; either open the pressure relief valve on the tank or turn on the hot water in a sink. Either one will let air enter the tank and allow the tank to empty. This can take an hour or more - be patient and let the tank drain completely.
Elements are generally too tightly screwed in to loosen with pliers, and a will be needed; by far the most common size is a 1½ inch socket. This is not an item common in most homeowner tool kits and one may have to be purchased just for this task, but it is far cheaper than hiring a plumber or replacing the entire hot water heater. If you already have a ½" drive socket set you may need just the new socket and an adapter to fit the smaller drive but if not you may need to purchase a "breaker bar" to go with the socket. large socket wrench
Remove the wires to the heating element and, using the 1½ inch socket, unscrew it an remove it from the tank.
Make sure there is a rubber gasket on the new heating element and screw it into the tank. It may be difficult to get started as the end inside the tank is heavy and it will tend to tip down. Make sure you don't "cross thread" it as you start the threads into the hole. Screw in a few threads by hand before using the socket wrench. Tighten securely and refill the hot water tank with water. Be sure and leave the hot water turned on in the sink until water, not air, comes from the faucet. If the power is turned on without the tank being completely filled it will promptly burn out the new heating element; these elements are not designed to operate in air, but only when completely submerged in water. Check for leaks around the new heating element.
Giving it some time, verify that the tank is operating properly and producing hot water. Turn the power off and replace the thermostat covers, insulation and access panel covers. Turn the power on for a final time.
Replacing the Thermostat
The hot water tank need not be drained for this operation but it is easy to forget where the wires go, particularly on the upper thermostat. Take a photo or draw a picture of where each differently colored wire goes or mark the wires themselves.
Remove all the wires, followed by the thermostat itself. Mount the new thermostat the same way the old one was secured, and re-attach all the wires. Adjust the temperature according to directions on the new thermostat - a good setting is 120° on the upper thermostat and 110° for the lower thermostat. Check and set both even if only one was changed. Turn the power on and, giving plenty of time, verify that the tank is operating properly and producing hot water.
Turn the power off and replace the plastic thermostat covers, the insulation and the access covers. Turn the power back on for the final time.
Troubleshooting hot water tank heating and elements, along with replacing any that are bad, isn't a particularly difficult task. A voltmeter, a phillips screwdriver and maybe purchase of a large socket wrench can save a plumbers call. Learning to do simple home repair tasks can save a world of hassle with contractors and a good deal of money.
Changing the Heating Element
Questions & Answers
© 2011 Dan Harmon