How To Test A Thermocouple With A MultiMeter Quality Tips #1

How a Thermocouple Works | Thermocouple Testing Procedure Understanding

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

How to Test a Thermocouple with a MultiMeter