My gas fitter has just replaced the thermocouple on my heater....what does it do?
A thermocouple is a temperature sensor on a gas heater that acts as a safety device by monitoring the presence of a flame. It generates a small voltage when exposed to heat, which keeps the gas valve open. If the flame goes out, the voltage decreases, leading to the closure of the gas valve and the cessation of gas flow, ensuring the safe operation of the heater.
The thermocouple is typically positioned near the pilot light.
Here's how it works:
- Pilot light ignition: When you turn on the gas heater, a small gas flame called the pilot light is lit. The pilot light serves as the ignition source for the main burner.
- Heat generation: The pilot light generates heat, and part of that heat is directed towards the thermocouple.
- Voltage generation: As the thermocouple junction is exposed to heat, it produces a small voltage known as the thermoelectric voltage or electromotive force (EMF). This voltage is a result of the temperature difference between the hot and cold junctions of the thermocouple.
- Safety function: The generated voltage is used as a safety measure. It is connected to a safety valve or gas control valve in the gas supply line. The voltage acts as a signal to keep the gas valve open, allowing gas to flow to the pilot light and main burner.
- Flame monitoring: If the pilot light goes out or the flame is extinguished for any reason, the heat reaching the thermocouple drops. As a result, the thermocouple generates a lower voltage or no voltage at all.
- Safety shutdown: When the voltage drops below a specific threshold or ceases to exist, the safety valve or gas control valve receives this signal and closes, shutting off the gas supply to the pilot light and main burner. This prevents the release of unburned gas, reducing the risk of a gas leak and potential hazards.
So the thermocouple is a very important little part on your heater!
Remember to always use a gas fitter licensed in Type A Gas Appliance Servicing and have your heaters serviced & safety checked at least every two years.
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