How To – Fixing An Electric Water Heater That Is Getting Too Hot – Thermostat

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    It may sound strange but one of the problems when your water heater malfunctions is that it can allow the water to get too hot.

    The reason this happens is because the thermostat on your water heater has malfunctioned and it is allowing the heating element to remain on at all times instead of cycling on and off as heat is needed.

    The symptom for this problem is steaming hot water coming out of your faucets which can scald you in just seconds.

    The problem its self may go unnoticed in the summer months when you limit your use of hot water and you may find that your electric bill is 20 or more dollars higher then normal for the month.


    Now this is not the simple problem where your hot water is just too warm and you want it to be a little cooler so you can save some money but if you do want to turn down your water heater’s temperature setting we cover that at the very end after installing a new thermostat.

    Before You Begin

    Before you begin you will need to know how to turn your water heater off at your circuit breaker box. Water heaters are normally hard wired directly from the circuit breaker and take a 220 volt circuit to run. You may have a smaller point of use unit that can run on standard 115 volt but in either instance you need to turn it off at the circuit breaker and not at a timer or other device that you may have installed between the heater and the circuit breaker. The amount of amps going through a 220volt line will definitely pack a punch so be safe.

    After you have turned the water heater off you can begin your inspection.

    Initial inspection

    After the power has been cut to the water heater you should begin by inspecting the main electrical feeds into the unit. Make sure that they are not extremely hot or melted. This is not normal to happen but it is possible. If they are very hot to the touch .. so hot that you can not touch them then you may need to replace the line if the shielding has melted. You would probably know that this has happened if the circuit breaker tripped to the off position however you may have caught it just before final failure so inspect the feed line.

    Next you want to remove the access plates that will provide you access to your electrical parts.

    Some units have just one heating and thermostat access plate others have two. If your unit is 60 gallons or larger it probably has two heating elements and thermostats.

    Visually inspect the wiring and thermostats for melting and burnt areas. Again like your main line it is not normal to see melted parts or wiring but you need to inspect them because you will need to turn the power to back on to perform tests on your thermostats and heating elements.

    Beginning Your Tests

    Testing a water heater is pretty simple as you see there are only a few parts that can go bad no matter what problems you are experiencing.

    The basic parts include:

    The Tank – which could rust and then you would see leaks

    The main wires into the unit – it is possible you could have a short between the unit and circuit breaker.

    The Heating Elements – if they go bad you will either have No heat, less heat or overheating.

    The Thermostats – similar to the elements you could have no heat, less heat or overheating.

    The internal wiring – either no heat or less heat.

    What you need for your tests

    You will need a hand held volt meter with an ohm setting. The tester must be able to read AC at the required voltage of 115 or 220 volts for home units or three phase for commercial units.

    You will also need a flash light and a couple good screw drivers philips and flathead to remove the access plate, detach wires and remove parts.

    A diagram of your specific heater’s wiring layout.

    There are about 6 different ways that your water heater could be wired. This will depend on if you have a single or double heating element unit and if the elements can turn on independently.


    Seems pretty easy so far doesn’t it … Yea  well it is.

     Testing The Heating Elements

    Since your water heater is off you want to perform your ohm tests on your heating elements now.

    Set your meter to OHMs and then remove the wires from your heating element.

    It is best to test only one element at a time so you don’t forget which wire goes where.. Also pull the wire to the side when you remove it so it is on the side of the screw it attaches to.

    Touch both probes to the screws that hold your wires in place and the reading should be close to zero. This means that your elements have a good element rod that is allowing all of the voltage to pass through it.

    Next touch one probe to your wire screw head and one to the base of the element. The nut part where you put a wrench on it to remove it. You should have a high reading showing a lot of impedance meaning the electricity is not grounding out because your heater element has corroded and is shorting.

    Your manufacturer should give you specific readings for your tests. Follow their directions for replacement.

    When you are done remember to tighten your wire connections.

    Testing Your Water Heater Thermostats

    Since our problem is with overheating it is very likely that both the heating elements will test ok. However like said above a shorted element could possibly cause overheating.

    Since this system has an upper and lower heating element and Two thermostats we need to follow the manufacturer’s directions closely when taking our voltage tests.

    Where the previous tests were done with the power to the water heater turned off these tests will need to be performed with the power on. If you do not think you are capable of taking these readings yourself without causing yourself injury hire a professional.

    First double check that the wires to your unit are connected correctly then turn the Thermostats to their lowest setting.

    When you turn the thermostats down all the way this is done while there is hot water in the tank. This will mean that the heating elements should not have electricity passing through them. This is important for the test because you want to see if the thermostat is malfunctioning and allowing electricity to the elements in a normally off condition. This would cause overheating if the elements are always getting power.

    In our case we first check the top thermostat by touching the probes between the #2 screw /wire and the exit wire on the thermostat.

    The top thermostat checks ok and shows no power reading on our meter.

    The bottom element is checked in a similar way. Following manufacturer’s direction we see that there is power 220 volts on our meter. Because there is power even with the thermostat on the lowest setting AND very hot water in the hot water tank this means that the thermostat is not sensing the temperature of the water and turning off the lower heating element.

    Replacing A Bad Water Heater Thermostat


    Do it now because your water heater is overheating and you want to limit the possibility of damage to an element or other problem.. Leave it off until you have replaced the thermostat.


    Most water heaters allow you to replace their parts with Generic parts available at most home centers and supply stores. This means that you do not need to order a special thermostat or heating element if one goes bad.

    Gas water heaters that are slightly more complex also have some generic parts that can be found at most better hardware stores.

    There are two basic thermostats that you can buy. The top thermostat in most water heaters accepts the main power connection and passes electricity to the top element and also down to the lower thermostat. As you will see there are more wire connections and it is about twice the size as the lower thermostat.

    The lower thermostat only controls the lower heating element and has two wire connections.

    When you go to the store they will have two bins of thermostats. Pick the one that matches your needs.

    NOTE I do not suggest that you bring the thermostat with you when you buy a new one because you will want it to stay attached to the water heater until you are ready to replace it.Then when you replace the new thermostat you can transfer one wire at a time to the new thermostat so you do not mix up which wire goes where. This is more important for the upper thermostat then the lower because of the number of wires but … don’t take chances the store will only have two types of thermostats to sell you and they are easy to recognize.

    To remove the thermostat you will need to remove the wires and pull back the metal clip that holds it in place. Some thermostats may have screws to hold the housing in place if so remove those screws.

    Inspect the new thermostat and look for numbered terminals.

    When you remove one wire if possible attach it to the new thermostat. However most of the wires will be cut to exact lenghts so you probably will need to insert the new thermostat before you start attaching wires. If you are the forgetful type take a picture or make a drawing and use masking tape to number the wires.

    On the bottom thermostat you can see that the dial to set the temperature has moved from the top to the bottom but the wires are in the same place.

    After you have attached all of the wires and double checked the screws for tightness double check that the thermostat has a good ground and is fit tightly in the retaining clip.

    As you will notice the ground wire for the lower thermostat and element is attached to the retaining clip. This means everything should fit tight .. no lose thermostats…

    Turning the Power Back On

    You are now ready to test your work.

    Turn the thermostat to its lowest setting and turn the power back on at your circuit breaker box.

    Return to the water heater and set the temperature of the thermostat by turning the screw clockwise.

    While turning the screw towards a hotter setting listen for a CLICK when the thermostat reaches the temperature in the tank.

    This means power is now going to the heating element and the water inside is getting hotter.

    Then back the heat setting down below that point until you hear it click again.

    This means the heating element is OFF.

    You can try relying on a temperature setting on the thermostat but they rarely are accurate. As you can see our new thermostat has a 125F setting however our old thermostat just said Hot —-> Hotter.

    It is a bit of hit and miss and you will need to recheck your water temperature after 24 hours and make it hotter or colder as you like.

    Final Note

    As you can see repairing your Water Heater is not a really technical or difficult job but it can be dangerous working with live voltage to make tests. You must have a steady hand when using your volt meter probes and good light. You should also have experience working on a live circuit.

    REMEMBER THIS IS 220 VOLTS .. and you are in twice the danger as you would be working on a light switch or electrical outlet in your house that was Live… AND YOU NEVER DO THAT DO YOU???..!

    Honestly this is not the hardest thing to do but you must be extremely careful as if your life depended on it because it does.

    IF YOU HAVE ANY DOUBT of your ability DO NOT DO THIS YOURSELF.. hire a technician.. pay them $60 for an hours labor.

    Use this howto to double check their work… and to know you are not getting ripped off.

    It is VERY unlikely that if your water heater is overheating that you will need new elements OR that more then one thermostat will go bad at a time.

    Thermostat replacement does not require draining of your water heater BUT heating Element replacement will require you drain your tank.

    Thermostats cost between $10 and $20 for the part depending if you are replacing a small bottom one or a top one with more connections..

    And remember these parts are generic.

    So, do it yourself and pay $9 like we did or get a professional to do it and pay $80 it is up to you and may be worth your while to hire someone just because water heaters are often stuffed into places you dont want to go… under stairs or crawl spaces or tight closets or even attics.

    But either way… BE CAREFUL.









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