Thermocouple Replacement


Replacing a Thermocouple can be both easy and daunting. It by far is one of the most important aspects within the Gas Heat System. It protects and provides a sense of security. It is very complex however very easy to understand. Thermocouples are made in different ways by different manufacturers however, all have the same basic principle, stop the gas when the flame is out! That’s it! Nothing else.

How Does It Work?

The Thermocouple is based on heat, gas and expansion. Ever noticed how on a gas product you must first hold down the pilot valve, light the flame then wait 10-20 Seconds? Well this is placing the thermocouple in operation. As you hold down the pilot valve gas is emitted. The flame then heats the end of the thermocouple and as that flame heat it creates an expansion effect or a direct heat effect. The gas filled area is beginning to expand due to the heat (Remember Heat Cause Expansion) and as that gas expands it then creates a very small voltage. This voltage is presented on the valve side of the thermocouple. Some use a bellows and others do not but it’s all the same theory. With this gas expansion or conduction of heat the main gas valve is then open feeding gas to the flame. When that flame goes out, the gas then cools and contracts causing the main gas valve to shut stopping the flow of gas therefore creating a safety for our systems. As long as this small voltage is producing the flame will stay lit.

What Appliances Have Thermocouples?

There are many applications that use thermocouples but remember any Gas served systems will have a thermocouple or something that resembles such. Thermocouples can be found in Gas Heat Systems, Water Heaters and many different other gas fired systems.

How Do I Check My Thermocouple?

Thermocouples should be checked only by qualified technicians as they are a very vital component of the systems not only operationally but as a safety mechanism as well. When a technician checks he uses a voltmeter to monitor the DC Millivolt outputs to see if the thermocouple is working properly. Typically DC Volts that are less than 20 indicates that the thermocouple should be replaced. As a key note thermocouples typically produce 30 Millivolts of power.

As a Technician What Will I Learn?

You will learn how to remove access panels, be able to read the incoming power supply to the unit and the differences between DC Volts and AC Volts. You will be required to identify the Main Gas Supply, Electrical Breakers and the different components located on the unit you are servicing. You will have to have in-depth knowledge of different special tools none more important than the voltmeter. Safety is always a concern as you will be dealing with Gas, Electricity and moving parts. Always wear proper Personal Protection Equipment when servicing or troubleshooting any type of HVAC equipment or even other appliances.

A HVAC Technician should be able to troubleshoot and evaluate a thermocouple after being trained on how to replace a thermocouple.