Sit 0290204 termopar

This thermocouple is listed under the Sit brand with catalogue article 900.799.071 and manufacturer codes 0.290.204 and 900.799.071. It belongs to the category of thermocouples and thermopiles. Thermocouples of this type are used on atmospheric gas appliances to perform flame detection. Unlike ionisation or UV/IR sensors that communicate with a burner control, a thermocouple generates a small millivolt signal from the heat of a pilot burner or main flame. That voltage holds open a safety valve; if the flame goes out, the signal drops and the valve closes, cutting off the gas supply. Parts of this kind are selected primarily by their physical length, the type and orientation of the tip (straight, angled, or formed to fit a specific pilot burner position), and the connection to the safety valve. The thermocouple is mounted so that its hot junction sits directly in the pilot flame, and its cold junction connects to the valve through a threaded or push‑fit terminal. When replacing a thermocouple of this class, check the overall reach from the mounting point to the flame. A contaminated or carbon‑covered tip will degrade the signal; a broken sheath or a loose connection at the valve will also prevent reliable flame‑holding. Because the millivolt output is low, any corrosion or poor contact in the circuit will cause nuisance lockouts. Ensure the pilot burner is clean and that the flame impinges correctly on the thermocouple tip.