Your furnace's thermocouple is usually located right in the flame of the furnace's pilot light. Its copper tubing makes it easy to spot. The thermocouple is made up of a tube, a bracket, and wires.
A type K thermocouple has one red wire and one yellow wire. Type K thermocouples have a useful temperature range of negative 200 to 1,250 degrees Celsius. A type J thermocouple has one red wire and one white wire. Type J thermocouples have a useful temperature range of 0 to 750 degrees Celsius.
Thermocouples are sensors used to measure temperature. It is a device used inside a gas furnace in Kansas, to assist the pilot light in keeping your furnace running and safe. It works rather like a fail-safe to keep unburned gas from accumulating and burning, exploding or causing another type of health risk.
After about a minute, when you're sure the probe has gotten hot, place one lead on the shaft of the thermocouple and the other lead on the connector. If the reading is less than 25 millivolts, the thermocouple is bad and needs to be replaced.
It's easy to replace and a new one costs $5 to $10. Rather than trying to unfasten the thermocouple inside the water heater's burning chamber, it's easier to remove the whole burner and thermocouple assembly.
Whereas a J Type Thermocouple is made up of iron and constantan, K type Thermocouples are composed of a nickel/chromium alloy (chrome) and a nickel/aluminium alloy (alumel) which gives them much better protection against oxidation and acidity than the iron limbs of the Type J.
A Type K thermocouple refers to any temperature sensor containing Chromel and Alumel conductors, that meets the output requirements as stated in ANSI/ASTM E230 or IEC 60584 for Type K thermocouples. This may be an immersion sensor, a surface sensor, wire or another style of sensor or cable.
The point where the thermocouple is connected to the copper connections of an instrument is the cold junction. Either a precision RTD or thermistor is used to measure the temperature at that point.
After enough time, metal fatigue can cause a thermocouple to break. Thermocouples that are regularly exposed to extreme heat stress or extreme conditions are more likely to go through metal fatigue. If thermocouples start to give out unusual readings, it may be suffering from metal fatigue.