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.
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Repairing a Heater
- 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.
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).
- In the provided picture, the meter indicates 0.078 volts present. This is less than 1/10 of a volt, and is considered “off”.
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.
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”.
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.
- Lower access panels removed, exposing the plastic shock protector:
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.
- 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.