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What's a Water Heater Thermocouple?

What’s a Water Heater Thermocouple?

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A thermocouple is a sensor that measures temperature. A water heater thermocouple is an important safety device inside your gas-fueled water heater, preventing both explosions and the dangerous release of uncombusted natural gas.

Most traditional gas water heaters have a standing pilot light that burns continuously. When the temperature inside the water storage tank drops below the set temperature, the thermostat triggers the gas flow to the main burner. In order for the gas valve to open, however, the thermocouple must signal that the pilot light is burning and hot enough to ignite the gas.

The water heater thermocouple itself consists of two pieces of wire, welded together at one end, inside a protective covering. It looks like a length of copper tubing, with one end attached to the thermostat. The other extends into the main burner where the tip, or sensor, is positioned within the pilot light flame. As the wires inside the tube heat up, they produce a tiny amount of electricity. When the temperature gets hot enough to ignite gas, the thermocouple sends an electric signal that opens the gas valve. If the pilot flame goes out, the thermocouple cools down, the signal stops and the gas valve automatically closes.

Does your water heater have a thermocouple?

Many newer, energy efficient water heaters have electronic ignition instead of a standing pilot light and thermocouple. They contain solid state controls that only ignite the gas burners or pilot when the storage tank needs heat. Look for the copper tubing. If you don’t see it, your gas water heater has electronic ignition.

Water Heater Thermocouple Problems

Water heater thermocouples are reliable and safe, but they do wear out. Because of the constant heat to which they’re subjected, carbon builds up on the wires inside the copper tube and the thermocouple fails. Suspect a broken thermocouple if

  • You can’t light the pilot light at all
  • The pilot light won’t stay lit
  • The main burner won’t stay lit.

Because of its design, a thermocouple has no parts that can be repaired. It can easily be replaced, though, and replacements are available at home supply and hardware stores. Most residential water heater thermocouples are interchangeable, but a few water heater brands accept only their own brand. Check with a plumbing professional if you’re not sure what to look for, or if you want help working on a gas-fueled appliance.

Thermocouples have been used in millions of gas appliances, all over the world, for many years. They’re designed for safety, even when they fail. You can count on your water heater thermocouple to help keep your home safe.

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