Heater repairman: Ran out of hot water? You can easily repair (and replace if necessary) the controls and heating elements of most common residential 120, 208 and 240 volt electric water heaters with traditional line voltage controls; not the microprocessor types that are starting to appear in stores. Further, it does not discuss gas or propane fuel types nor plumbing related issues. This is a detailed, comprehensive article with additional help on the discussion page.
Heater repairman
Repairing a Heater
Shut off the power. Most water heaters are supplied by voltages that can cause shock, burns and even death should an energized conductor come in contact with the body. Shut off power in the electrical panel by removing fuses or by moving the handle of a switch or circuit breaker dedicated to the water heater to the Off position. Completely remove and “pocket” the fuses or otherwise secure or lock the panel and place a note on the cover to alert everyone that work is being performed on the water heater circuit. This will prevent the accidental energizing of the circuit while you are working on it.
Heater repairman
Clear away any insulation blocking access or view of the controls (thermostat and high-temperature switch) and heating element. Once the thermal insulation has been removed, plastic shock protectors are visible. Carefully fold any wires away from the protective cover. Lift the tab at the top away from the clip and remove to access terminals.
- View with plastic shock protector removed:
Look for obvious signs of damage. Water heaters can leak as a result of a failing tank – but also due to poorly fitted or soldered cold water supply pipe / hot water output pipe or a poor seal between tank opening and heating element. If allowed to continue to leak, it will cause internal damage to the controls should water enter them.
- Rust coats wires and controls – both outside and inside
- Rust is conductive – even when on the wire insulation. This can lead to potentially deadly shocks, heating and melting insulation and even burns. Sooty, black carbon deposits on surfaces indicate a short circuit. Chances are there is an exposed copper wire that may be difficult to see due to the carbon deposits that resulted from the short circuit.
- Wires may have been damaged and now suffer with a reduced circumference that is needed to safely carry the heating element electrical load. This point of damage also becomes a source of heat. It is very important to repair or replace all parts that have visible forms of water and short circuit damage. This includes wires, wire insulation, jumpers and the controls themselves. As mentioned above, rust is a conductor and provides unintended and unexpected paths for electricity. These unintended paths can be dangerous and make troubleshooting very difficult to perform.
- Here, the yellow wire between the control and element appears to have shorted to the tank (or other metal) leaving a sooty black deposit on the wire and above. Notice the lower left terminal of the thermostat. Excessive heat has caused the plastic around the terminal to begin to melt.
Heater repairman
Locate the parts below:
- High Temperature Limit Switch: Has a reset button There will be (4) terminal screws / wires connected to it. Usually, the top two terminals have wires that go up to the field wiring compartment that bring the power to the rest of the water heater’s controls and heating elements. The “upper controls” consist of the High-Temperature Limit Switch and Upper Thermostat. The “lower controls” refers to the Lower Thermostat (there is no High-Temperature Limit Switch for the lower section of most electric water heaters). Three of the four terminals are numbered and visible in the picture (#1, #3, & #4; the #2 terminal is not identified as it is connected directly to the thermostat below via factory installed jumper).
Measure Voltage. Set the AC voltage range to the highest available. Touch the probes to the top terminals of the high temperature limit switch as shown in the image to the right. If desired, the range may be lowered to any desired – provided the range is greater than the voltage displayed at the highest range. If unable to prove power off, double check circuit panel. Do not proceed unless power is proved off; otherwise damage to meter is likely and shock or burns is possible in the steps that follow.
- In the provided picture, the meter indicates 0.078 volts present. This is less than 1/10 of a volt, and is considered “off”.
Heater repairman
Set the multimeter to Ohms or Resistance. Observe the meter indication. If an analog type, the needle or pointer will be resting at over the higher resistance values (left-most position) this is an “open circuit” indication. If digital meter is used, it may display “OL” or “1” (“1” without trailing or leading zeros). This OL or 1 indication represents a value greater than the meter is capable of displaying (similar to the way a calculator does) for “overload” or “infinity”. Infinity in high resistance range is also called an “open circuit” or “Open Loop” (OL). Take note of this open circuit indication for this meter (when in a voltage or current range is selected and the meter displays OL or 1, the measurement should be taken again after adjusting the range upward). If you are unsure what your meter should read in an “OL situation”, just leave the terminals unconnected to anything and not touching each other and switch the meter on, it should then indicate the resistance of the air between the terminals which should be infinity in normal conditions.
Set the range (if provided) to R x 1. If the meter being used does not provide for range selection, it is likely an “autoranging” type. This simply means that the meter will automatically adjust the range up or down as needed without any intervention by the user. This feature is far more common on digital meters than analog types. Most analog meters that do not provide manual range selection likely support only a single range. These meters are much more accurate indicating low values (such as 0 through 500k or 1M ohms) than higher values (such as those above 1M), but will work well for this procedure. Pay close attention to the display of an auto-ranging digital meter when reading – there is a huge difference between 20, 20K and 20M ohms. A “K” indicates thousands, and an “M” indicates millions. The examples above would correctly be read as 20 ohms, 20,000 ohms (20K ohms or 20 kilo ohms) and 20,000,000 ohms (20 meg ohms or 20 million ohms). Each is 1000 times larger than the previous.
Heater repairman
Press the metal tips of the test probes together. The analog meter pointer should move to lowest values of the resistance scale (or fully to the right). The digital meter should indicate 0 or a “very low” value approaching zero. Locate the “Zero Adjust” knob and turn so that the the meter indicates “0” (or as close to “0” as possible). Most digital meters do not have this Zero Adjust feature. Once “zeroed”, this needle position on the dial is the “short circuit” or “zero ohms” indication for this range of this meter. The meter must be zeroed if the resistance range is changed. Measured resistance values will be inaccurate if unable to properly zero the meter.
- In the example picture, the meter indicates 0.2 ohms resistance – or zero. The meter can not display a value lower than this value, since there is no zero adjust feature it is considered 0.
Replace batteries if needed. If unable to obtain a zero ohm indication on an analog meter, this may mean the batteries are weak and should be replaced. Retry the zeroing step above again with fresh batteries. Digital meters often graphically display the battery’s level of discharge or simply an indication to replace the battery. Check the meter manual for help determining the battery charge state.
Press the probe tips against the terminals of the heating element (one probe to each screw). Read the meter display. Look for a range multiplier (a “K” or “M” in the display) to be sure the value displayed is really ohms, not kilo ohms (K) or meg ohms (M).
- In the provided picture, the meter indicates 12.5 ohms resistance, and since is within acceptable limits of the calculated 12.2 ohms value, it is considered “good”.
Heater repairman
Be aware that a “good” heating element will read a very low value (between 10 and 20 ohms depending on wattage of the element and possibly read as 0 ohms depending on your meter). To determine the resistance value for a good element, use this online calculator. Provide the voltage (likely 240)and wattage (likely in the range of 1000 to 5000) ratings from the nameplate and click on the “calculate button”.
- The picture displays the “nameplate” information of the water heater. Two different wattage ratings are provided (4500 / 4500 and 3500 / 3500). The “4500 / 4500” rating is the wattage rating for the upper and lower element respectively, when connected to a 240 volt supply. Alternatively, the “3500 / 3500” rating is the wattage of the upper and lower element respectively, when connected to a 208 volt supply. Most residential applications are 240 volts, but 208 volt and 120 volt types are also found.
Check for a grounded element. Prepare the meter by setting the meter to highest resistance scale.
Hold the probes at the end of the test leads together. The analog meter pointer should move fully to the lowest values of the resistance scale (to the right). The digital meter should indicate a “low” value very close to zero. Locate the “Zero Adjust” knob and turn so that the the meter indicates “0” (or as close to “0” as possible). The digital meter may not have this Zero Adjust feature. Note that this position is the “short circuit” or “zero ohms” indication for this particular resistance range of this meter. Always “zero” the meter when changing resistance ranges.
‘Repeat the steps needed to gain access to the lower thermostat and heating element.
- Lower access panels removed, exposing the plastic shock protector:
Heater repairman
Remove protector as done for upper access point above to expose the terminals. Notice that there is no reset button (high limit) on the like the top:
Set the bottom thermostat to minimum.
Set the range of the meter to the lowest Voltage value that is greater than 240 Volts “AC” or “VAC”. As mentioned earlier, common voltages for residential (and mobile home / RV) type water heaters are: 120, 208 & 240, with the most common being the 240 volt variety. When steps below discuss measuring “line voltage“, substitute the voltage for your particular water heater instead.
Check the top heating element’s terminals for presence of line voltage by touching a probe tip to each terminal, as done in the resistance test earlier. Line voltage is likely 120, 208 or 240 in the U.S.
- The line voltage in the system under test is 208 volts. Since 203 is within a few percent of 208, this example indicates full power available to the element and if it passed the resistance or ohms test above – is heating the water in the tank.
Heater repairman
If no power, trouble is an open circuit. Check the heater’s “field wiring compartment” (usually located on the top of the heater), along the length of the cable that feeds the heater, and lastly inside the electrical panel. Remember, unless power is shut off at panel, this circuit is live at some point between the fuse or circuit breaker and the water heater. Tighten any and all wirenuts and connections in the wiring compartment and inside any junction boxes between here and all the way back to the terminals of the circuit breaker or fuses in the electrical panel. Replace open fuses or reset any tripped circuit breaker if off. Check for power at fuse or circuit breaker. A circuit breaker that immediately trips after resetting indicates a short circuit or less likely, defective circuit breaker.
Heater repairman
Once the water in the top part of the tank has reached the temperature value determined by the top thermostat setting, the top thermostat (is considered “satisfied”) switches power from the top element to the lower thermostat. If the temperature of the water in the bottom part of the tank is higher than the lower thermostat’s setting, the lower thermostat remains “off” and voltage is prevented from reaching the lower heating element. If however, the temperature of the water in the bottom part of the tank is lower than the setting of the lower thermostat, the lower thermostat switches “on” and sends voltage to the lower heating element (a thermostat that has switched power to a heating element or cooling compressor is said to be “calling”) and heats the water.
Heater repairman
The easiest and quickest way to do this is to allow hot water out of the tank by simply opening a hot water faucet. Cold water will enter the bottom of the tank and mix with the existing hot water in the tank, lowering the overall temperature.
Heater repairman
If line voltage found, check for line voltage at heating element terminal screws by touching each probe to the terminal screws.
Heater repairman