They are used primarily to prevent the dangerous release of natural gas within a residential environment, which could cause an explosion, fire or even death if inhaled over an extended period of time.
A water heater thermocouple is designed like a standard type K thermocouple, composed of 2 dissimilar metal alloy wires that are welded together at one end to measure and monitor temperatures. Water heater thermocouples are installed on the exterior of the water tank and often have a dial that allows altering of the temperature settings, although when most measure heat that generates a current of 20 millivolts or less, the gas is automatically turned off.
Thermocouple instruments for water heaters are connected by a series of metal tubes to the pilot light and main burner, and can easily be replaced if needed. They are seen in almost every residential or smaller commercial building such as offices and stores that have a hot water system which is heated by gas. Some newer systems have replaced a standing pilot light and thermocouple with solid state controls that are operated by electronic ignition.
The main purpose of a water heater thermocouple is to ensure the pilot light of a water heating system is working properly. The pilot, which ignites the main gas burner used to heat the tank reservoir, ensures that the gas is immediately ignited and does not build up within the tank, a safety hazard that is likely to end in an explosion. As a temperature sensor, the thermocouple monitors whether or not the pilot light is burning by sensing the temperature or heat being produced. If it has stopped burning, the thermocouple stops the flow of gas before it is able to build up at the burner head.
The thermocouple is mainly composed of two wires of differing metals that are joined at a junction that forms a sensor tip. This sensor of thermocouple wire is positioned directly into the hottest part of the pilot light’s flame. The wires are protected by a metal covering and travel to a thermostat which measures the temperature. The heat of the pilot light produces an electric current that travels down the wires. If the thermocouple measures the current and determines it is hot enough, it sends a signal to the gas supply, causing it to open, or remain open. If the heat is too low, the gas supply is turned off. Like other thermocouples or temperature sensors, those used in water heating systems are very reliable, ensure safety and last for long periods of time.