Close this search box.

Thermopile Voltage Low – What To Do?

Note: This post may contain affiliate links. This means that at no cost to you, we may receive a small commission for made purchases.

Thanks to modern technologies and simplified systems, it has become relatively easy to install and maintain a water heater.

Almost all heaters come with good indicators and documentation to help you in the setup process. However, every once in a while, you may come across some issues, and thermopile voltage low can frustrate the hell out of you.

Here is the bigger problem if you ask us: beginners may not understand the concept of thermopile and what the thermopile voltage low message means.

We know this because we have been there too. So, this article is a quick guide on what to do when you see the thermopile voltage low on your water heater system.

We have explained the basic ideas about thermopile and how it works. We will begin by answering the most obvious question.

What is Thermopile?


In the context of water heaters and other heating appliances in general, a thermopile is a collection that may bring together many thermocouples.

These thermocouples do one of the necessary tasks to keep the water heater running. As you may know, a modern water heater controls the temperature of the outgoing water through an electronic system.

This electronic system, which is made using circuit boards, needs a specific amount of current to get started. Thermocouples are the part of the heater that provides this basic current.

Depending on the water heater model, a thermopile can have different designs and features. At the core, however, a thermopile stays the same. You do not have to worry about it at all.

If a thermopile is in a working condition, you would not have any problem getting hot water out of the water heater — at the preselected temperature levels.

The problems begin when a thermopile cannot work in the way it should. That is also when you start seeing the issues and error messages. And the most common error would be the thermopile voltage low situation.

What Does Thermopile Voltage Low Mean?

error codes on termopile

From the example below, you should understand that a thermopile should work properly if you need a water heater to function correctly.

If the thermopile does not generate the correct voltage, the heater may fail to provide you hot water. So, this is what the thermopile voltage low error means.

The error means the thermocouples in the collection cannot generate enough current to power the control panel that we mentioned. If this happens, the controller system will stop working, and you will see an error message on the water heater.

The error gets the name because you would not get the correct water supply due to a faulty thermopile system. If you happen to see the thermopile voltage low error often, it means there is some problem with the primary thermopile system.

Most water heaters would show you a list of status light codes. The machine may flash a specific light multiple times to help you identify the problem. For instance, the indicator light may flash three or four times when the thermopile voltage is low.

By looking at these indicators, you would understand whether your water heater has this problem. However, as much as these systems are accurate, you should check the efficacy of a thermopile once again.

And, this is when you have to think about testing a thermopile on your own. This extra testing will confirm whether you have to replace the thermopile.

How to Test Thermopile?

termopile voltage measure

Before we talk about replacing the thermopile, we need to ensure if the current one is working. Sometimes, a loose cable or a problematic circuit may prevent the thermopile from working.

Anyway, you can follow the steps we have mentioned below to test a thermopile. Keep in mind that you need a couple of tools to test a thermopile. Most importantly, you need access to one of the accuracy-oriented multimeters.

As you may have guessed already, a thermopile creates only a minimal voltage. So, the multimeter should be precise enough to record that.

  1. The first step is removing the thermocouple from the water heater. You should be able to do this by following the safety instructions provided by the manufacturer.
  2. Even though you can perform several tests to understand whether the thermopile is working as it should, we recommend going for the closed-circuit test. You have to perform this test, and it would tell you whether the thermopile can handle the load.
  3. Now, you have to connect the red positive lead of the multimeter to the red thermopile wire. On the other hand, you can join the black-colored lead to the white wire of the thermopile.
  4. Now, you have to turn on the power or gas supply. You will have to press the gas supply button for a while as the multimeter takes the reading.
  5. This process may take a couple of minutes, and the multimeter would slow down once it has finished the reading process. In the end, you can see the measurements on the screen as well.

Here are the specifications you should keep in mind. Your thermopile is working fine if the reading is between 650 and 850. However, if you see that the reading dips below that, you will have to replace the system.

If the number is below 400, you may have to replace the thermopile system altogether. Once you have confirmed that the thermopile requires replacement, we will move to the next steps.

How to Replace Thermopile?

replacing termopile

It is the step-by-step guide to replacing the thermopile. However, you should know a thing or two about these steps before you jump in.

First of all, replacing the thermopile is not an easy job. We are not saying that it is rocket science, but it does not mean you should take it lightly. Depending on your expertise with all things electric, replacing the system may require a few hours.

However, if you hire a professional electrician, they might finish the job in an hour or so. It would be best if you did not have those expectations, though. Therefore, if you cannot stay patient and learn from the mistake, you should hire a professional to replace the thermopile.

If that is not the case, you can follow the steps below to replace the product.

  1. As you can guess, the first step is to turn off the power supply. After this, you can remove the central cover, which will expose the components inside.
  2. It would be best if you kept in mind that water heaters may have sensitive wiring inside. Keeping this in mind, you have to disconnect the wires leading to the ignitor and the thermopile.
  3. You can spot a manifold door assembly in the system. You have to capture a photo of how the water heater has arranged the wires. After this, you can remove the manifold fold.
  4. Once you have done this, it will be easy to remove the pilot assembly and the thermopile wire. To do this, you may have to unscrew the pilot assembly in the first place. If you are dealing with the correct cables and proper sensitivity, you can get the wires out in a few seconds.
  5. Now that you have gotten the old wires out, you have to place the new thermopile wires in. However, when you do this, you will have to align it with the manifold door. You can also set up the wires to go through the manifold system.
  6. After this step, you can set up the Manifold component block. While this setup requires you to add a few screws, you should be sensitive about how much pressure you apply. You should ensure that the added wires are not touching each other.
  7. Once you have set up the manifold component block, you can also connect the thermal switch wiring, which should not take long. Right after this, you can reattach the manifold door as well. You can say if you have done this job right by listening to the click sound. In any case, you will have to add a few more screws to the package.
  8. Now that you have set up everything, you can connect the pilot tube back. Keeping in mind how the original thermopile was placed in the system, you can connect the thermopile wiring into the place. To test if everything works fine, you can try pushing the ignitor switch. You should be able to see the pilot light if everything went well.
  9. If you did see the pilot light, it means you have done a great job. You can now turn on the gas supply and adjust the system’s temperature as you wish.

As you can see, the process is a little too detailed. Here is a tip that can help you. Try to take as many photos as possible when you remove the original thermopile. These photos will come in handy when reinstalling the systems and arranging the wires properly.


We hope we answered the more important questions you had about thermopile voltage low situations.

Even though we have added step-by-step instructions, you should check the safety instructions provided by the maker of the water heater. Otherwise, you may encounter issues in running the water heater for long-term needs.

author avatar
Charlie Hardcastle


On Key

Related Posts

Is Drano Bad for Pipes? The Truth Revealed

Note: This post may contain affiliate links. This means that at no cost to you, we may receive a small commission for made purchases. When it comes to dealing with clogged drains, many homeowners turn