This 2-in-1 Hi-Limit and Temperature sensor screws into several models of Astrel Easy Heater.
It is a single sensor with two plugs, which both plug directly into different locations on the control system motherboard. The two-pin plug is for the "hi-limit" protection (saftey cutoff in case of overheating), and the four-pin one is for the temperature sensor functionality.
There used to be a Hi-Limit only version of this sensor (part number 10A546A001), which had just a single two-pin plug, but that sensor has been discontinued. Astrel advises you to use the 2-in-1 sensor in its place, and leave the temperature sensor plug disconnected.
Sensor diameter: 6 mm
Plugs: one two-pin for Hi-Limit and one four-pin for temperature.
Astrel: 10A546A003 (replaces 10A546A001)
Jacuzzi & Teuco: 233005730