De Dietrich 300009745 termostato di sicurezza 105C

De Dietrich safety thermostat with a nominal switching temperature of 105 °C. Catalogue article 336.805.001, also listed under manufacturer code 300009745. Safety thermostats of this type serve as a limit device in the heating system. They are normally wired in series with the burner control circuit and interrupt the burner supply when the water temperature exceeds the set point. Unlike NTC sensors that send a variable resistance signal to the control board, a safety thermostat operates as a simple on/off switch. Selection for replacement must consider the switching temperature, reset type (manual or automatic), and the mounting arrangement – immersion or clamp-on. The probe form and electrical connection must match the existing installation. When replacing such a thermostat, verify the temperature rating against the original part. Common failure modes include a stuck contact that fails to open, or a drifting set point that causes nuisance trips or no protection. Also inspect the probe condition – if clamp-on, ensure good thermal contact with the pipe. The cable and connector should be intact and free of corrosion.