WHAT IT DOES:   
 
Typically, when you power up the sensor  the board looks at both Over Heat 
Sensor and the Temperature Sensor and compares them. It should see no 
significant difference and the range should be within normal range. If it see 
outside the tolerances, depending on which system you have, it will notify you of 
the problem and fail to turn the spa on. If the temperatures are close, it continues 
it’s self test. 
 
To Replace: 
 
The Temperature sensor inserts into the filter box. Simply pull down and the seal 
will break and the sensor will come out. If you have water in the spa, it will pour 
out. You usually can switch with the new sensor fast enough to minimize water.  
 
The Over Heat sensor clips on the heater. Again, simply pull out. 
 
Connection to the board: 
 
The most common connection of the sensors to the board is a joint plug where 
both the temperature and high limit sensor pair together. To release the wires 
from the plug do this: Unfold a paper clip. Note on the plug the ends of the wires 
inside the plug are rectangular windows. By pressing down on the wire 
rectangular ends and pulling the wire, the end will release from the plug and slide 
out exposing the ends. 
 
If you have black ends to your cord there is a simple clip to press to release. The 
biggest problem is the clip is hard to see and sometime to reach. If you look on 
the top of the clip you will see the lever to press down to release. I use a small 
screwdriver to press down and pull out..