Sensor located in a 50 mm flue gas pipe that measures draft from the suction side. The sensor has two prongs equipped with measuring resistors. 1 prong transmits the resistance value, and two receive. If a prong has broken off, e.g., during cleaning, the alarm ”NO FLUSSO” or ”ALL CLEAN CHECK UP” appears on the fireplace display. The sensor is easy to replace by using cable ties for mounting. In the newer model sensor, a large mounting rubber is included instead of the old two small ones, and the mounting orientation of the sensor is 45°, whereas the old one was vertical.