Thermostat Probes

Mercury-containing thermostat probes may be found in several types of gas-fired appliances that have pilot lights, such as ranges, ovens, clothes dryers, water heaters, furnaces, or space heaters.

Mercury thermostat probes, also known as flame sensors, gas safety valves or pilot thermocouples, are most commonly present as part of the safety valve that prevents gas flow if the pilot light is not lit. In this application, the bulb of the thermostat probe projects into or near the pilot light. These are commonly present in gas ovens and may be present in any other appliance with a pilot light. A mercury thermostat probe may also be present as part of the main temperature controlling gas valve. In this application, the probe is in the air or water that is being heated and is not directly in contact with any flame. These are typically found in older ovens, clothes dryers, water heaters, and space heaters.

The metal probe consists of a metal bulb and thin tube attached to a gas-control valve. The mercury is inside the tube and expands or contracts to open and shut the valve. Although non-mercury thermostat probes have been used in these appliances, you should treat all probes as though they contain mercury, unless you know that they do not.

Look for tags or labels that identify the thermostat or thermocouple probe as containing mercury. In most cases the repairperson will take the replaced units and properly dispose of them. Recycling is the proper method of disposal. DO NOT throw mercury probes in the trash. If you need further information, visit the Brown County Household Hazardous Waste Facility at 2561 S. Broadway or call the Recycling Hotline, (920) 448-4400.