The after-market thermistor kit (1 control and 1 hi-limit sensor included with o-rings) that fit with either the 4kW or 6kW after-market PDR Titanium double-barrel heater. These sensors plug in directly to the motherboard located inside the control box. Adapters are available if you have an older style control box.
Note: ALWAYS REPLACE THE THERMISTORS IN PAIRS. If a new thermistor differs in temperature sensing more than five degrees from the old thermistor, the system will go into a “fault mode” and prevent the heater, jet pump(s) and light from operating.So again, when replacing a control thermostat thermistor always replace the high limit thermistor as well and vice versa.
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 does 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.