How to Test a Thermopile with a Multimeter

This site contains affiliate links to products. We may receive a commission for purchases made through these links.

Congratulations! You have just completed installing your new water heater, allowing you to save a huge amount of money by doing it by yourself. It is nearly time for you to celebrate your success with a long, hot, and relaxing shower.

But before you do, you head to check your heater one last time and find that the pilot light is out. Of course, there should be some error, so you reset the pilot light right away. After a few minutes, it goes out again. You now get a blinking red code, which informs you the thermopile voltage is low.

What does that technical term imply? How can you fix it? It might take a few technical skills to get to the root cause of the problem for a DIY homeowner. That’s a common concern for most water heaters. 

What Does It Indicate?

Keep in mind that having a basic awareness of how your water heater works could be very beneficial. Let’s dig deeper to discuss what it implies to come across low thermopile voltage.

When we talk about your water heater, the pilot often lights up the thermopile. As this happens, they generate a tiny voltage of electricity passing over to the gas control valve. A pilot light could not be available.

When that occurs, it means there’s no electricity, shutting down the gas control valve until the light is lit again. The mechanism needed to relight the pilot light will depend on how old or new your unit is. 

What is a Thermopile Exactly? 

If you didn’t know yet, a thermopile is a device converting thermal energy into an electrical signal. It’s composed of different thermocouples linked in series or sometimes in parallel, each of which has two diverse materials with a massive thermoelectric power and differing polarities.

The thermocouples are often placed through the cold and hot areas of a structure, and hot junctions are thermally secluded from the cold junctions. Also, the cold junctions are normally located on the silicon substrate, offering an efficient heat sink. 

In hot areas, you will find a black body for absorbing the infrared, increasing the temperature based on the incident infrared’s intensity. 

What are the Different Uses of a Thermopile?

Thermopiles are used to present output to the temperature variation as a part of the temperature sensing system. For instance, it’s used in accelerometers to distinguish the temperature profile in a sealed transducer’s cavity or in infrared thermometers used in medical applications to determine the body’s temperature.  

Aside from playing a crucial role in water heaters, there are many applications for thermopiles. Some of these include, but not limited to:

  • Automatic exhaust gas analysis
  • Aircraft fire and flame detection
  • Fire recognition in transportation tunnel
  • Automatic HVAC control
  • Blood glucose monitoring
  • Black ice detection and early warning
  • Security human presence and detection
  • Commercial building lighting and HVAC control
  • Thermal line scanner
  • Handheld non-contact temperature measurement 

They are also used in gas burner controllers, heat flux systems, and pyrheliometers for safety purposes. The system’s output is normally between ten to hundreds of millivolts. It may also be utilized to deliver special temperature averaging in the form of boosting the signal situation.

Thermopiles also create electrical energy from the solar wind, radioactive materials, radiation, laser combustion, or heat electrical parts. The process of producing energy is also an example of electric current moving from heat water or also referred to as the Peltier phenomenon. 

Keep in mind that thermopiles are utilized to give an output in response to the temperature. That’s very critical in a water heater where you like the water to come out at a specific temperature standard. You won’t be able to enjoy that relaxing steamy shower that you’re used to if your thermopile voltage is low and the pilot light is out. 

That’s why testing your thermopile is very necessary. 

How Do You Test a Thermopile for Functionality?

Would you like to test your thermopile to determine if the setting is low? Lucky for you because the process is quite straightforward and simple. You can test your thermopile in a few minutes with the right tools. All you need to use is a digital multimeter.

  1. Set up the multimeter for direct current. Make sure you also set it to millivolts or for less than one volt.
  1. Disconnect the thermopile wiring connection from the gas control. You may need to wiggle it a bit before it becomes loose.
  1. Attach the red positive lead to the red thermopile wire, and the black negative lead to the white wire. 
  1. Set your gas control to pilot lighting setting. Then, light it according to the directions from the manufacturer. Check the owner’s guide for certain instructions on lighting your pilot light. Take note that each model and make might be a bit different. At this stage, the voltage on your multimeter will begin to increase.
  1. Hold down the thermostat knob of the gas control until the maximum voltage is met. That might take at least three minutes or more. You will know it’s done when the reading on your digital multimeter slows down. 

Remember that a healthy thermopile in an open circuit test will often read between 650 to 850 millivolts. Your thermopile needs a replacement or service if the read is below 400 millivolts. 

Final Thoughts

Indeed, dealing with a thermopile problem in your water heater could be a huge pain. Further, it takes quite a bit of technical know-how and skill. On top of that, you will need to invest in specialized tools and spend a day working hard to fix your water heater.

You may like to find that the time investment is well worth the money you saved from a trusted professional repair. Still, you want to make sure you don’t incidentally cause damage to your unit. 

We hope you find this post informative and helpful. The next time your thermopile seems strange to you, consult this article again for your testing steps.

Special offer for our visitors

Get your Soldering Iron Guide For DIYERS

We will never send you spam. By signing up for this you agree with our privacy policy and to receive regular updates via email in regards to industry news and promotions