How to tell the difference between a thermocouple and a thermopile?

Author: Mr. William Marks MD  |  Last update: Friday, August 1, 2025

Thermocouples are generally skinny and pointed at the top with a copper tube ending in a threaded connector. Thermopiles are generally wider and will have actual wires leading off the body to screw onto terminals. Thermopiles are also interchangeable with other thermopiles.

Will pilot stay lit with a bad thermopile?

No. If the thermocouple is bad, the system sees the failure as a pilot light gone out, and shuts off the gas.

How can you tell the difference between a thermistor and a thermocouple?

A thermistor is a thermally sensitive resistor that exhibits a continuous, small, incremental change in resistance correlated to temperature variations. Thermocouples reflect proportional changes in temperature through the varying voltage created between two dissimilar metals electrically bonded together.

How do I know what thermocouple I need?

Because a thermocouple can take many shapes and forms, it is important to understand how to correctly select the right sensor. The most commonly criteria used to make that choice are the temperature range, the chemical resistance, the abrasion and vibration resistance and the installation requirements.

What is the difference between a thermocouple and a thermopile?

The main difference between Thermocouple and Thermopile is their method of measurement. The thermocouple is a thermoelectric instrument, while the thermopile is an instrument that modifies thermal energy into electrical output.

Thermopile vs Thermocouple

How to identify type of temperature sensor?

If there are 3 wires, two red and one white, it is almost certainly a 3 wire Resistance thermometer. A third wire could also be a sheath grounding wire, while the other two are a thermocouple. If there are 4 wires, two red and two white, it is probably a 4-wire resistance thermometer.

How do I identify a thermistor?

Identifying thermistors and RTDs

Thermistors and RTDs feature either two, three or four wires that are red and white, or red and black. The red wire is the excitation, while the black or white is the ground.

What are the signs of a bad thermocouple?

The Pilot Lights But Won't Stay Lit

If the flame lights and goes out when you release the gas control knob after holding it in for the recommended 20 to 30 seconds, that's the sign of a thermocouple malfunction.

Can a thermocouple replace a thermopile?

They are not interchangeable with each other although they are similar, they do two different things in gas-fired systems.

Should pilot flame touch thermopile?

Your pilot should be about 90 percent blue, with very little yellow. It should also be touching the surrounding sensors such as the thermocouple and thermopile. If the color of the flame turns yellow or red, it's a sign of gas contamination.

What is the life expectancy of a thermopile?

As long as they are used correctly and maintained properly, thermopiles can last for years or even decades and remain in good working condition.

How many thermocouples does a thermopile have?

Thermopiles can be constructed with a single thermocouple pair, composed of two thermocouple junctions, or multiple thermocouple pairs.

How to identify thermocouples?

You can easily identify a thermocouple type by the colors of its wire insulation. In this video we'll be focusing on the ANSI wire color coding used by the United States and Canada. In ANSI color coding, the red wire of a thermocouple is negative, and the positive wire is color coded to the type of thermocouple.

How do I know if I have an RTD or thermocouple?

The Clues to Tell the Difference

For example, if the temperature sensor has three leads, the sensor is an RTD. Thermocouples only have two leads. On the RTD with three leads, almost always two of the leads will have one color and the third lead will have another color.

How can I tell what temperature sensor I have?

Start by checking the wiring diagram / schematic. Temperature sensors are very different in physical appearance, electrical connections, and purpose. Additionally, a lot of other sensors have a temperature sensor on the side, because they need protection, or their reading must be temperature-compensated.

Can a thermopile be cleaned?

I used a combination of a cheap stainless steel brush, some 000 extra-fine steel wool, and some fine grit sandpaper to remove as much baked-on soot as possible from the thermopile, and I figured I may as well clean the thermocouple while I was there.

Which can be detected by a thermopile?

Hence, Infrared radiation can be detected by a thermopile.

Are thermopile universal?

Universal Thermopile Works With Most Gas Fireplaces – Fire-Parts.com.

What are the 2 wires for on a thermocouple?

A thermocouple consists of two dissimilar metal wires coming together to create a temperature measurement junction. Heating the connection point of both metals creates a thermoelectric current known as a Seebeck current.

What is the color code for sensors?

3 & 4-Wire DC Sensor Connections

The brown wire is connected to the positive side of the DC power supply, the blue wire is connected to the common (or minus side) of the DC power supply, and the black and/or white wires are connected to the die protection control or sensor interface.

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