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What you will learn from How to Test a Thermocouple with a MultiMeter article:

 

  1. How not to guess if the thermocouple is bad
  2. Step by step procedure for testing a thermocouple with a multimeter
  3. What reading you should get if the thermocouple is good. The millivolt thermocouple range.
  4. The thermocouple testing procedure.
  5. Lots of resource and related links to help you learn more

How to Test a Thermocouple with a MultiMeter? What is the thermocouple millivolt range for a good thermocouple?  What is the thermocouple test procedure? So you have found the pilot light will not stay lit when you try to light the pilot light. You know you have gas, and everything seems to be fine so what is the problem? That will help with a furnace thermocouple test. It also is good for water heater thermocouple testing.

How to Test a Thermocouple with a MultiMeter

You ask a friend, and the friend tells you the thermocouple is bad. So, the next question, “How to Test a Thermocouple with a MultiMeter”?

So how do you test the thermocouple to see if it is bad or not? You will need a multimeter that will read millivolts (most meters read small voltage like millivolts, which is 1/1000th of a volt) and a source of fire such as a lighter or small torch. How to Test a Thermocouple with a Multi-Meter step by step:

How to Test a Thermocouple with a MultiMeter

Thermocouple fits securely in the pilot burner (pictured above)

How Do I Know My Thermocouple is Bad?

MultiMeter Thermocouple Test Procedure

  1. First, remove the thermocouple.
  2. Secondly, turn on the meter and set it to Ohms. Touch the two leads together from the meter, and you should get a reading close to zero. With the leads apart, you will read infinity. That is simply a test to check the meter for continuity. Finally, NOW TURN THE METER TO VOLTS.
  3. Thirdly, start the flame and put the tip of the thermocouple in the fire.
  4. Next, ensuring the tip is nice and hot from the flame, take one lead from the meter and put it on the shaft of the thermocouple and the other lead and put on the end of the thermocouple where it makes contact with the gas valve.
  5. Finally, if the reading is less than 25 millivolts replace the thermocouple as most standing pilot gas valves need 25 or more millivolts to keep the pilot flame lit. The thermocouple millivolt range should be above 25 millivolts. If so then it is good.

How to Test a Thermocouple with a MultiMeter

If you test the thermocouple with the multimeter and you get a reading above 25, then you have another issue. Importantly, always make sure the tip of the thermocouple is directly in the pilot flame. If the tip is in the flame, you have held the nob on the gas valve down for longer than a minute, the pilot flame is strong and steady, and the pilot still does not stay lit, then you likely have a problem with the gas valve. Lastly, Gas valves cannot be repaired as per any manufacturer. You need a new gas valve. Finally, Good luck!

How a Thermocouple Works | Thermocouple Testing Procedure Understanding

Thermocouple Testing Procedure

A thermocouple is a safety device for a standing pilot gas system. Originally, it had a ratio of copper and nickel and was labeled a Coppel (Copper/Nickel) element. Thomas Seeback discovered it in 1821. In the early 1900s, Honeywell applied it to the safety gas valve.

A standing pilot gas valve has two inner valves, one for the pilot light and one for the main valve. If the pilot valve is closed the main valve would not open. The thermocouple was used to hold the pilot valve open. Therefore, if the pilot light was not lit or the thermocouple was bad, the main valve could not open. That provided a means of proving the main burners would ignite when the main valve opened.

The tip of the thermocouple is called the hot junction and is where the two dissimilar metals join. A weld joins the two metals. The other part of the thermocouple tip is called the cold junction. From the cold junction, a stem runs in length from the main body of the thermocouple tip to the gas valve.

When the heat hits the hot junction or tip of the thermocouple, it produces millivolts. This fractional voltage energizes a small solenoid designed for millivolts. As long as the solenoid is energized, the pilot valve inside the gas valve remains open. That allows the main valve inside the gas valve to feed the main burners with gas.

Conclusion | How to Test a Thermocouple with a MultiMeter

Since this is gas and there is a possible safety issue if you feel uncomfortable doing this call a professional. Plumbers and HVAC service companies are skilled and knowledgeable with standing pilot gas systems. They can troubleshoot the problems and replace the thermocouple if necessary. If you are interested in other examples of troubleshooting standing pilot systems including thermocouples here are few resources for you:

Gas Valve Troubleshooting | How To Light a Pilot Light | Why Does My Pilot Light Keep Going Out

High Performance HVAC Air Conditioning and Heating Systems

How to Test a Thermocouple with a MultiMeter

Use our handy calculator to see how many BTU's your natural gas appliances are producing:


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