OH message - overheat protection tripped

[daxel_bob]

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?

[MaryH]

It is a very good indication that your temperature sensor is failing. Usually when the temperature on the display is not matching what the actual water temperature is on the spa then it is usually the temp sensor. There should be a wiring diagram on the control door that will show you where the temp sensor plugs into the circuit board. You can then follow that cable to see where the sensor is mounted.