The thermocouple in a gas furnace is designed to keep the gas valve open through its electric voltage. If the pilot light goes out, the loss in heat causes the voltage between the two pieces of metal to drop, and this shuts the valve and reduces the combustion risk.

What are the advantages of thermocouple?

Advantages : ? Temperature range : Most practical temperature ranges, from cryogenics to jet-engine exhaust, can be served using thermocouples. Depending on the metal wires used, a thermocouple is capable of measuring temperature in the range – 200°C to + 2500°C.

What is the principle of thermocouple?

The operating principle of the thermocouple is based on the Peltier effect. The thermocouple circuit consists of two metals joined together to form two junctions of different temperatures. A Peltier emf is generated due to the difference in temperatures of the two junctions of the circuit.

What is the voltage of a thermocouple?

Thermocouple Voltage-to-Temperature Conversion Method

Temperature Input Voltage Output
-100°C 0VDC
+1350°C +5VDC

Are thermocouples universal?

Universal Thermocouples. Universal thermocouples, as the name implies work on most water heaters. They are available online and in home supply stores for a reasonable cost. The length and the thread type are the two concerns when purchasing one.

How long do thermocouples last?

Thermocouples can last several years, but they don’t typically last as long as the furnace itself. If the pilot remains lit, but the main furnace doesn’t stay lit, it’s time to replace the thermocouple. Replacement thermocouples are in stock at most hardware and home improvement stores.

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Besides, how do I know if my thermocouple is bad?

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. Before jumping to the conclusion that the thermocouple is at fault, look at the pilot flame.

Can a thermocouple be cleaned?

If the Thermocouple is faulty it will cause the unit to shut down. How to clean? Remove Thermocouple from pilot assembly, using steel wool or emery cloth to lightly clean the tip removing any soot or build up that might have accorded due to an improper pilot flame.

Subsequently, question is, how does a thermocouple produce electricity?

A thermocouple is an electrical device consisting of two dissimilar electrical conductors forming an electrical junction. A thermocouple produces a temperature-dependent voltage as a result of the thermoelectric effect, and this voltage can be interpreted to measure temperature.

How many millivolts does a thermocouple put out?

The normal millivolt output is 25 to 35 millivolts; on some, you may even get up to 35. The other part of this safety pilot system is the electromagnet (power unit). It is if you will the LOAD and we can say the thermocouple is the SOURCE.

Do thermocouples need to be calibrated?

Consequently, thermocouples require calibration to ensure accurate temperatures are derived. It is essential to check your thermocouples regularly and periodically, to ensure they are appropriately and accurately calibrated to maintain correct, repeatable and high-quality temperature measurements.

What is the difference between RTD and thermocouple?

The RTD is more accurate than a thermocouple. However, an RTD is limited to temperatures between 500 and 932 degrees F. Generally speaking RTDs are more expensive than thermocouples, but actual instrument, wiring, and installation is generally less, so makes up for some the cost difference.

Can you jump out a thermocouple?

Harley said: Bypassing the thermocouple would make it no more dangerous than any propane grill. It’s not going to make it explode. The only thing it would prevent is losing a tank of propane into the atmosphere if the flame happened to go out because the valve wouldnt close.

Similarly, it is asked, how do you fix a thermocouple?

Replacing a Thermocouple

  1. Shut off the gas and electrical power to the furnace.
  2. Remove the furnace’s access cover.
  3. If the furnace has been running, wait 30 minutes for the thermocouple to cool completely.
  4. Unscrew the nut that holds the thermocouple end fitting into the gas control valve, using an open-end wrench.
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Why does my thermocouple keeps burning out?

1) Faulty Thermocouple. If your pilot light won’t stay lit, the thermocouple is very likely the culprit. The thermocouple is the copper rod the pilot flame directly hits. Sometimes it’s referred to as the “flame sensor.” It’s a safety mechanism that shuts the gas off should the pilot go out.

What does a thermocouple look like?

The thermocouple looks like a piece of metal tubing smaller than a soda straw. To find it, first locate the gas control box. This is the box that the main gas line enters, where you turn the gas on in the furnace. The other end of the thermocouple sits in the flame of the pilot light.

How do you test a thermocouple?


  1. Locate the pilot light controls on the gas valve.
  2. Turn the pilot light on for 30 seconds.
  3. Release the button to see if the pilot light goes out.
  4. Turn off the gas supply to test the thermocouple again.
  5. Count to 20 and wait for the pilot light to go out.
  6. Listen for clicking near the gas valve.

Which type of thermocouple is best?

Type K Thermocouple (Nickel-Chromium / Nickel-Alumel): The type K is the most common type of thermocouple. It’s inexpensive, accurate, reliable, and has a wide temperature range. Accuracy (whichever is greater): Standard: +/- 2.2C or +/- .

How many types of thermocouples are there?

Thermocouple Grade Wire

Calibration Type Temperature Range
K 32 to 2282°F 0 to 1250°C
E 32 to 1652°F 0 to 900°C
T 32 to 662°F 0 to 350°C
R or S 32 to 2642°F 0 to 1450°C

What causes a thermocouple to fail?

Changes in temperature can cause regular expansion and contraction in metal, which will cause thermocouples to weaken over time. After enough time, metal fatigue can cause a thermocouple to break.

Does the length of a thermocouple matter?

The length of a thermocouple has no effect on its measurement accuracy or its ability to transfer the signal to the instrument. In other words, thermocouples do not experience “voltage drops” or power loss along its length as a high current power line might possess.