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The thermocouple of a water heater is a safety device to prevent the risk of gas leaks. Although it has been replaced by a more modern system on recent models of gas water heaters, this technology is still used on many installations. Explanations.

What is the thermocouple of a water heater?

Gas water heaters are equipped with a night light and thermocouple. The latter is an essential device since it ensures the safety of the device. The welding that crowns the device is made with two different materials, a detail at the origin of this name of thermocouple.


  • The thermocouple is used to check that the flame of the night light rest always on. To ensure this function, it is installed near the latter.
  • When the tip of the thermocouple heats, it generates a current to identify the heat produced by the pilot, which attests to its proper operation.
  • Thus, when the flame of the night light comes to go out the arrival of the fuel is (almost) instantly cut off. This avoids dangerous gas leaks.

To note: All new models of water heaters are no longer equipped with a thermocouple, the latter having been replaced by a electronic ignition and an ionization probe.

Thermocouple maintenance of a water heater

To ensure its safe function, the thermocouple must be regularly maintained, like all components of the water heater.

A meeting who must intervene when:

  • your water heater often turns off
  • the night light can not stay on;
  • the night light does not come back on at all.

Before thinking about having the device replaced, it is sometimes very useful to disassemble it to recover the thermocouple and clean it (with special attention to its tip).

However, when a pilot goes off too regularly, there is a good chance that the thermocouple has reached the end of its life. It must then be replaced by a new one.

For this, two options are available to you:

  • replace it with an identical thermocouple model;
  • use a universal thermocouple.

Warning: Before working on your water heater, remember to turn off the appliance ("off" position), turn off the gas supply and turn off the power supply.

Video Instruction: How To Install / Replace a Thermocouple in a Hot Water Heater