The thermocouple in heating and cooling refers to a copper probe that sits right in the flame of a boiler, hot water heater or gas furnace. It is used to communicate with the gas valve and signal when the flame of the device has gone out. If the flame goes out the gas valve shuts down so that there is not gas leaking into the area. If gas continued to run through without a flame to burn off the gas, the gas could easily cause a fire, explosion or cause gas poisoning to those around it. This thermocouple is an extremely important yet small device that needs to be working properly in order to ensure that the gas is not leaking into the building. This can be a major hazards and cause exceptional damage.
Replacing a gas coupling that is not working properly is not a job for anyone other than a professional. If the old one is removed improperly or the new one is installed incorrectly, there could be the potential for grave danger, even explosion. A professional in heating and cooling or a master plumber are the professionals that you should contact if you need a new thermocouple in your building. You want to be sure that they have experience in replacing this type of a device and that they are able to handle it. They will need to turn off the gas while they accomplish the goal and then turn it back on when they are finished.