Hi @mpking,
What is the [https://intexcorp.com/replacement-parts/spas/|model series] of the spa?
This is to know if replacement sensors are even available.
Don't know the tub and cannot find a service manual but how many wires are attached to each sensor?
usually sensors are just thermsitors which are resistors whose resistance varies with temperature.
There are two types. NTC negative temp coefficient - as temp goes up resitance value comes down and PTC positive temp coefficient as temp goes up resistance value goes up.
If there is only one wire then the control board is measuring the resistance value of the thermistor with regard to earth. Try removing the sensor and connecting an Ohmmeter between the wire connection terminal on the sensor and a bare metal part on the body of the sensor. Then either cool down the sensor (ice) or warm it up (hair dryer?) and check what happens to the resistance.
If two wires then it's just measuring the resistance value of the thermistor.
Remove the sensor and measure directly across the two terminals with an Ohmmeter whilst either heating or cooling etc.
Usually manufacturers use the same type of thermistor for all applications and not different ones in the one product so the measurements should be very similar.
Just what I'd try.