I have a vita spa that was given to me. Not sure how old it is. 10 years maybe? The model is vintage type is LH. Electronics inside say Balboa. I looked for a manual on the vita spa website, but that model isn't listed. The problem with it is it gives an SN error on the controls and it won't heat. I imagine it is a sensor in there somewhere but don't know where to start looking. Any help would be greatly appreciated.

SN1= Hi-Limit sensor malfunction
SN2= Temp sensor malfunction

Hi-limit is usually strapped to the heater flo-thru, the temp sensor will be in the shell somewhere, trace the wires from the control.