This Control Thermostat Thermistor communicates the actual water temperature to the controller (control box motherboard) to shut off the heater when the spa reaches the target temperature. It is used on all 73859, 72469, 76840 and 76091 control boxes.
1. Set the meter to 20K on the OHM scale.
2. Record the temperature of the spa water.
3. Unplug the thermistor from the control box.
4. Meter across the two Thermistor leads.
5. Refer to the Temperature versus Resistance chart below to find the correct resistance value for the temperature measured. If the temperature and resistance do not match that of the chart, this test has failed and the thermistor must be replaced. Remember if the spa has been inactive, the spa water temperature may be different
than the water temperature in the heater housing.