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The open circuit test reading of a thermocouple flame sensor is critical for ensuring safe and effective operation of gas appliances. The typical output voltage of a healthy thermocouple flame sensor is usually around 20-30 mV when it is detecting a flame.

This range indicates that the sensor is functioning properly and responding effectively to thermal changes caused by the flame. If the reading falls within this range, it confirms that the thermocouple is generating the correct amount of voltage due to the presence of heat, which is essential for the safety mechanisms of gas systems.

Lower voltage readings, such as those in the 1-2 mV or 5-10 mV ranges, would suggest issues with the thermocouple or inadequate flame detection. Similarly, significantly higher readings, such as those in the 50-60 mV range, could indicate potential malfunction or miscalibration of the sensor. Understanding these voltage ranges is crucial for troubleshooting and ensuring the reliable operation of gas appliances.