Chosen Solution
The Base Unit (dated 2019) SB-H10 (the one without the tall stalk) is displaying water temps of 120-140 degrees. In reality, the water is 65 degrees. Obviously, the temperature sensor is “broke”. But which one is it to replace? I’ve had the unit apart, and I’ve removed three sensors, cleaned them, and put them back in. I’ve also left it unplugged for about 6 hours. There are two sensors with hex head, that seem to bolt into the top and bottom of the heater. and there is one on the plastic discharge pipe (this one does not appear to actually go into the water, and is only held in with a retaining arm). Finally, I don’t know if it’s a sensor, but there is a black wire wrapped like 60 times around the discharge pipe right before it goes back to the spa. So which sensor is the one I replace?
Hi @mpking, What is the 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.
