I have a 15 year old Marquis spa that is displaying an OH message which indicates that the spa has shut down due to an overheat protection sensor. Ever since refilling the spa this fall the thermostat has not been reading correctly. To keep the water temp below 106 (independent thermometer reading) the control panel has been set at 91. When the OH sensor tripped the water temperature was ~104. Do I just need to switch out the spa sensor assembly?