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Making Sense of Spa Sensors

Hot tubs have sensors in order to monitor and measure temperature and ambient conditions inside a heater tube or assembly.

Typically there are 2 types of sensors - a temperature sensor that keeps watch of the hot tub water temperature, and a hi-limit sensor that monitors the temperature inside the heater and lets the control system know if the temperature is above safe levels.   In the case of an OH overheat condition, the sensor communicates to the circuit board that the spa should no longer call for heat as a possibly dangerous situation has been encountered.   The proper operation of the hi limit sensor is necessary to avoid a heater dry fire or other dangerous condition. The proper operation of the temperature sensor (in either a dry or wet thermowell depending on sensor type), the sensor needs to measure the correct water temperature and pass that information to the circuit board/spa control system.

Finding a replacement temperature or hi limit sensor may be as easy as reading the model number of the sensor off of a little label/flag attached somewhere on the sensor wire.  Otherwise, the spa control system/circuit board may need to be identified in order to figure out which sensor(s) go with the particular spa pack.

Contact Hot Tub Outpost with your spa model information for assistance in identifying the correct sensors.

All electrical work on a spa should be conducted by qualified persons.

The technician may check the sensor wire(s) to be sure they are not chewed through by a rodent or otherwise damaged.  The connections to the circuit board should be firm.  Sometimes if there is a sensor error, the spa control system will show an error code on the topside control panel which can assist in troubleshooting.

M7 type sensors are those installed inside of a Balboa heater and control system.  This setup has 2 equivalent sensors both installed inside the heater tube.  They are available in 12 inch and 24 inch lengths.  When replacing an M7 type sensor, it is best to replace them both at the same time.

Some sensors can be tested with an ohm meter or a Balboa logic jumper on a stick tester in order to check resistance vs temperature.

See our hot tub sensors for a wide selection of spa sensor parts.