Master 4150.673 termopary BLP serii m

This thermocouple, listed under the Master brand as the 4150.673 BLP m-models, is a replacement part for use in air heaters and gas-fired appliances that rely on a pilot flame safety circuit. The catalogue article 696.799.006 and manufacturer code 4150.673 identify this specific variant. Thermocouples of this type generate a millivolt signal when heated by the pilot flame. This voltage holds the gas safety valve open; if the pilot flame goes out, the voltage drops and the valve closes, cutting off the gas supply. In a burner or boiler system, the thermocouple sits at the pilot burner tip, with its connection end running to the gas valve terminal. Selection is based on the thermocouple length (the distance from the flame to the valve), the thread size at the valve end, and the immersion depth—how far the tip extends into the pilot flame. The millivolt output must match the valve’s requirements; most standard gas valves operate in the 20–30 mV range. When replacing a thermocouple, check that the tip is positioned correctly in the pilot flame and that the connection is clean and tight. A loose connection or an oxidized tip can cause nuisance lockouts. Also verify that the pilot burner orifice is clean and that the flame envelops the thermocouple tip—approximately 10–15 mm of the tip should be in the flame. For BLP m-models, ensure the replacement matches the original length and thread type; do not rely on model numbers alone, as different configurations may use different thermocouple lengths.