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How to Test Heating Elements with a Multimeter

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Electric water heaters provide convenience and comfort around the house and other environments where they provide hot water for showering, dishwashing, and other applications. Today, more and more households are installing the systems due to the safety, low upfront, and maintenance costs. However, as it happens with many electrical systems, the heaters may fail due to various reasons. 

In most cases, a malfunctioning heating element, electrical system, or thermostat leads to the inability to heat water to the desired temperature. In particular, if one or more heating elements are faulty, you will notice that your water does not get hot as per the settings.

Electric water heating elements

The main work of the heating element is to convert electrical energy into heat. When electricity passes through, it will heat the surrounding water before it goes to the shower or another application area. 

Unfortunately, the electrical heating elements have limited lifespans. Most often, several conditions accelerate the deterioration hence reducing their service life. Some of the problems include mineral deposits in the water, air pockets, power surges, loose connections, faulty thermostats, and more. 

Common problems with the heating elements include burning up and breaking the continuity or short-circuiting and causing the heater to trip the circuit breaker or blow up the fuse. Also, the element material may deteriorate and increase the electrical resistance, resulting in the inability to heat the water to the set temperature.

Luckily, the elements are like consumables and, therefore, easily replaceable. That said, you need to test and ensure that the part is faulty before ordering a replacement. 

Rheem electric water heating element Image – Rheem

You have the option of calling a plumber or electrician when you cannot get hot water. However, before calling them or before ordering a replacement, you can do a few tests to determine if the elements are faulty. To do this, you need some basic technical skills and the following tools

  • Screwdriver
  • Non-contact voltage detector
  • Multimeter
  • Safety goggles
  • Gloves

Step by step testing of electric water heater elements

In practice, the elements are usually inside the water heater system. As such, it is not possible to inspect them visually. Moreover, the actual heating element has a metallic enclosure, so you cannot determine if it is working or faulty using your eyes unless it has severe physical damage. The best and effective way to test it is by checking the electrical continuity using a millimeter. Because of the voltages involved and the risks of fire and electric shocks, you need to follow various safety precautions. A typical step by step testing of a heating element is as below;

  1. Disconnect the power before working on the electric water heater. To do this, locate the water heater circuit breaker at the service panel and switch it off. If not sure about the specific breaker, turn off the entire electrical supply, assuming it will not affect other critical areas. Alternatively, use a multimeter or non-contact voltage tester to ensure there is no power at the supply input terminals.  
  • Drain the hot water in the heater. Open the hot water faucet while allowing the cold water to flow inside. Ideally, test the unit with lukewarm and not hot water. The process depends on the type of water heater and may not be necessary for some models. 
  • Locate and remove the access panel that covers the heating element. Note down the wiring to the element contacts and, if possible, draw the diagram. Loosen the screws and remove the wires from the element’s electrical contact terminals.  
electric water heating element connections
  • Check the wattage and voltage of the element. The information is usually on the nameplate or base of the heating element. To determine the electrical resistance value of the element, divide the square of the voltage by the power (watts) rating. 

            That is R= VxV /P or V2/P.  

            Where

R is the resistance

V the voltage rating

P the power rating in watts

Supposing the wattage is (P) is 3000W and voltage (V) is 240v, the resistance will be 240×240/3000 = 19.2 ohms. A good element should therefore have resistance around 20 ohms.

  • Set your millimeter to the resistance measurement and appropriate range, preferably the lowest where the calculated or expected value falls within. Please note that even if you cannot read the rating, the resistance is usually in tens of ohms and mostly less than 100 ohms.
  • Place one of the meter probes on the terminal where you have removed the wire. Put the other probe on the remaining terminal and read the result on the dial or display. If the element is functional, the reading will be closer to the figure you calculated in (4) above. Even when you have not calculated the resistance, most will read between 10 and 30 ohms.

A significant deviation indicates a faulty heating element, hence the need for a replacement. For example, a zero reading indicates a short circuit and will burn the fuse or trip the breaker. On the other hand, an infinite or very high reading (over 1000 ohms) indicates an open circuit, – which is the most common problem.

  • You will also need to test if the element is short-circuiting to the ground. To do this, place the probe on one of the contacts on the heating element. Take the second probe and touch its metal base, a metallic or grounded part of the heater system. Repeat this with the other contact. If you notice a low resistance, know that there could be leakage, and you need to replace the element.

When testing for current leakage, it is best practice to disconnect the two wires supplying the heating element.

Precautions when testing heating element

To prevent electric shocks, burns, or fires, switch off the power at the service panel before opening the unit. 

If you find a faulty element, ensure that the replacement part has exact physical dimensions and rating in terms of voltage and wattage as the broken one. For example, if you have a 120 volts element, never replace it with 240 volts even if they have the same wattage. The best practice is to take the faulty part with you so that the suppliers can give you a replacement that matches yours.

Before disconnecting the heating element, thermostat, or any other electrical component, note down or draw the wiring diagram to refer to when installing the new part. 

Conclusion

The electric water heater is an essential system in the house. It enhances the quality of life and comfort. However, the unit comprises various components that deteriorate or fail with time. One of the most common malfunctions is the inability to heat water to the right temperate, and it happens when one or more elements have failed. 

Luckily, with some basic technical skills and tools, you can test, identify and replace a faulty electric heating element. To do the test, disconnect the power and open the cover to access the element’s terminals. Remove the wires and use the multimeter to measure the resistance between the two terminals of the element. The electrical resistance is usually in tens of ohms, and if zero, very high, or infinite, the heating element is faulty and will require a replacement.