What is the minimum acceptable closed thermocouple reading?

The minimum acceptable closed thermocouple reading is 10 mV. This voltage indicates that the thermocouple is functioning effectively and detecting a sufficient temperature differential. Thermocouples operate on the principle of generating a voltage through the Seebeck effect, where a circuit made of two different metals produces a measurable voltage that correlates to the temperature difference present between the measurement junction and the reference junction.

Having a reading of at least 10 mV ensures that the thermocouple has enough sensitivity and accuracy to provide reliable temperature readings for safety and operational efficiency, especially in gas applications. If the reading is lower than this threshold, it may indicate a malfunction or that the thermocouple is not properly placed, leading to possible safety hazards or inaccurate temperature measurements in gas appliance operation.