Test Methods:
1. Turn off all power to the spa circuit breaker and spa components.
2. Set the ohmmeter to 20K, find the wire end and remove the plug from the circuit board.
3. Place meter leads on green and red wires.
4. Compare the reading to the thermistor resistance vs. temperature graph.
5. Most spa and hot tub caps (aka thermistors, thermal cutoffs, and temperature sensors) have a resistance reading of about 10,000 at 77 degrees Fahrenheit. Colder water will give higher readings up to 50K, while hotter 100°F water will give lower readings. Refer to the spa manufacturer's resistance versus temperature chart. Alternatively, if you get a "0" or zero reading, the sensor or cable may be damaged. Many hot tubs have multiple temperature sensors; a heater sensor, a water temperature sensor, and an air temperature sensor.