Thermopile Voltage Low – How to Fix It?

Thermopile Voltage Low On Water Heater

Thermopile devices are commonly used in heating devices such as gas furnaces, water heaters, and other heating devices. Sometimes, you may find that the connected appliances are not working correctly and have trouble heating or burning the water. These symptoms indicate a malfunction due to low thermopile voltage.

Cold junction faults, loose wires, and faulty internal units cause low thermopile voltage problems. Additionally, the location of your device, such as a windy area, can cause such voltage issues.

Before repairing a thermopile, you should know the meaning and working process of a thermopile. In this article, we go through the main aspect that develops this low voltage problem. Also, we provide you with a step-by-step method to solve the thermopile voltage low problem. Otherwise, an expert technician is the best option.

What is Thermopile?

In the context of water heaters and other heating devices in general, a thermopile is an assembly that can hold many thermocouples together.

These thermocouples play an essential role in keeping the water heater running. As you may know, a modern water heater controls the temperature of the outgoing water through an electronic system.

These electronic systems, built using circuit boards, require a certain amount of current to start. Thermocouples are part of the heater that supplies this primary current.

Depending on the model of the water heater, thermopiles can have different designs and features. Essentially, however, a thermopile remains the same. You don’t have to worry about it at all.

If the thermopile is in working order, you should have no problem getting hot water from the water heater — at the pre-selected temperature level.

The problems start when the thermopile does not work the way it should. This is also when you start seeing problems and error messages. And the most common error would be a low thermopile voltage situation.

Thermopile Voltage Low On Water Heater

Thermopile Voltage Low On Water Heater


As mentioned earlier, a special device can create a spark to relight the pilot. The pilot flame will then burn to a clear blue flame when the water heater has an air supply and sufficient gas pressure inside.

The pilot lights will perform some functions such as heating the thermocouple or thermopile, creating a small electric current that powers the gas control operation. This gives the necessary signal to the gas control valve that the pilot had turned on and reversed when the gas was released.

You should know that a thermopile is basically some thermocouples joined together. A thermopile can cause a higher current than a thermocouple. The thermopile will generate enough current to power the circuit board inside your electronic gas. Thus it can complicate heater operation conditions, issue error codes through LED light states, and control operation.

Thermocouples also produce a small current for the mechanical gas valve, but it does not have enough for the circuit board on your electronic gas control.

Testing a Thermopile

If you want to test your thermopile for damage, the process is relatively simple. Even if you have very limited experience working with gas and electrics, you can test your thermopile in just a few minutes with the right tools. All you need to get started is a multimeter that can read for millivolts.

  1. The first thing you need to do is set up your multimeter for direct current and set the range to less than a volt or set it to millivolts.
  2. Remove the thermopile wiring connector from the gas control. You may have to wiggle it a bit before it loosens up.
  3. Connect the red positive lead to the red thermopile wire and the black lead to the white wire.
  4. Set the gas control to the pilot lighting setting and light it according to the manufacturer’s instructions. Always refer to your owner’s manual for specific instructions on how to light your pilot light. Each makes and model may be slightly different. At this point, the voltage on your meter will begin to climb.
  5. Hold down the gas control thermostat knob until the maximum voltage is reached, which may take three minutes or more. You’ll notice this when your multimeter’s reading slows down.

A healthy thermopile will read somewhere between 650 and 850 millivolts or so in an open-circuit test. If the open circuit test reads less than 400 millivolts, the thermopile likely needs service or replacement. Be sure to consult your manufacturer’s manual to confirm this specification before proceeding with thermopile replacement.

Replacing a Thermopile

Replacing a thermopile typically involves the following steps:

  1. Safety precautions: Before you begin, ensure that the gas supply to the appliance is turned off and the unit has completely cooled down. It’s important to prioritize safety when working with gas appliances.
  2. Access the thermopile: Locate the thermopile within the appliance. It is usually positioned near the pilot light or main burner assembly. You may need to remove a cover or access panel to gain access to the thermopile.
  3. Disconnect the old thermopile: Identify the electrical connections attached to the thermopile. Depending on the specific appliance, there may be wires or connectors that need to be disconnected. Carefully remove any retaining screws or brackets holding the thermopile in place.
  4. Connect the electrical connections: Attach the electrical connections to the new thermopile, ensuring they are securely connected. Follow any specific instructions provided by the manufacturer regarding wiring or connectors.
  5. Test the replacement: Once the new thermopile is installed and connected, turn on the gas supply and relight the pilot light, if necessary. Test the appliance to ensure that the new thermopile is functioning correctly. Monitor the pilot light or burner flame to ensure it stays lit and provides the expected output.
  6. Finalize the installation: If everything is working properly, replace any covers or access panels that were removed earlier. Double-check that all connections are secure and that the appliance is in good working condition.

Please note that the specific steps may vary depending on the type and model of the appliance you are working with.


We hope you get the best possible answers to your query. Remember, several factors affect Thermopile current or its voltage reading. You can ensure low voltage using a multimeter. If the low voltage stays for hours, go through our troubleshooting steps, like fixing the cold junction, testing the unit, and replacement. Professional help is only required if no fixing steps work in your favor.

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