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Hot Springs Jetsetter w/intermittent heater problem

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I have a 2001 Jetsetter that has very inconsistent heating. It seems to 'forget'  to heat even though the Ready light is on. Today the water was 90 with the temp set to 104. But turning the power off and back on sometimes works to get it heating again. Also the temperature  does not correspond very well with the temp on the control panel, usually lower by several degrees or more. If I want 102 I have to put it way above that.  I have cleaned the thermistors which were pretty slimy and replaced the heater with  a spare I had. I know the heater works as it has gotten as high as 107. Could it be bad thermistors or maybe the mother board? Any other ideas I have may have missed?

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Have you tested the thermistors? Sounds like the sensor thinks the water is water then it actually is



  1. Run the jets, or the circ pump run so the water in the heater matches the tub
  2. Shut off all power to the spa at the breaker and spa pack
  3. Set your Ohm meter to the 20K setting
  4. Locate the wire ends and remove the plug from the board
  5. Place your meter leads onto the thermistors leads
  6. Compare readings to Thermistor Resistance vs. Temperature Chart HERE: http://www.backyardplus.com/pdf/thermistor-testing-chart.pdf

Most spa and hot tub high limits, aka thermistors, thermal cut-offs and temp sensors – will have a resistance reading of around 10000 at 77 degrees Fahrenheit. Colder water produces higher readings up to 50K, while warmer 100° F water will produce lower readings. Refer to your spa manufacturer resistance vs. temperature chart. Or, if you get “0”, or a zero reading, the sensor or cable is likely bad. Many hot tubs have more than one temperature sensor; a heater sensor, water temp sensor and air temp sensor.


So if the water is actually 90*, it should be read 7 K Ohms.

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