1)Hot Springs Soverign Hot Tub
2) 120VAC
3) IQ2000 Control Board

My Hot tub wont maintain a proper temperature. I have been troubleshooting this for nearly a year (I'm an electrical engineer). I have replaced both the temperature sensor and hi-limit sensor thinking it was that but it hasn't helped. The heater works fine, turns on and off when the heater relays fire everytime. Something in either the Main Board or the control unit is telling the unit to turn on/off at the wrong temps. I pulled the control unit and tested the Temperature Dial Reostat for proper resistance. Wasn't sure what to look for but there were no "dead spots" in the resistance measured. I will turn the temperature knob to a certain temperature, it will maintain temperature there for a few hours, (heater relays will turn off/on when they should) then the next day I will come out and the heaters will be fully on and the hottub boiling. I will then turn the temperature knob down and the heater relays wont click off till I move the knob a considerable amount. I then turn off the main breaker to the hottub, put the temperature dial to the original location, and the heater relays wont kick in anywhere near the same temperture.
Any Ideas? It's driving me nuts!

Is the tub getting hot enough to give you a high limit error? You've either got a bad reostat or sticky relays. If the heater is staying energized after the high limit trips then it would definitely be a relay issue, but otherwise it sounds like the thermostat dial.

I got my Fluke out at measured the reostats (both the Light Reostat and the Temperature Dial Reostat) and they both measure out to be about the same resistance through the length of travel. However they both increased in resistance to a point (about half of the overall travel) then decreased in resistance the rest of the travel. This seemed strange but both were doing it and the light works fine.

The Relays dont "stick" thats the strange part, they are only on when the Main Control Board "heat LED" is on, as soon as it shuts off the relays turn off.

I just let the tub run for two days and came out and the red power LED on the front of the tub was flashing red, I assume thats high temperature limit? I however didn't check to see if the heater turned off.

I am leaning towards a Thermostat dial, any way to rig the tub temporarly to bypass the temperature dial?