Hot Spring Spas 1992 – 2005 Hi Limit SensorHot Spring and Tiger River Spas 1995 2002 Hi Limit sensor. These sensors are commonly used in controllers pre 2002 and are plugged into the side of the box, if your sensor is plugged into the main PCB inside the IQ2020 box then you will require the following HS 39204. Sensor has a cable length of 970mm and a thread width of 12. 5mm(Smaller then the Temp sensor). It is recommended to also replace the Temp(control) sensor at the same time if replacing