cal spa temperature cant be raised higher than 99 degrees without tripping the switch

I have a cal spa 5000 it had a code (sf) and it wouldn't do anything cleaned and even took the filter out and it still had code so replaced the safety suction switch and that didn't work so he disconnected the pump and the heater and made sure they were clean and he plugged in the pump and it worked so he flipped the switch and then plugged in heater and it works except you cant raise the temperature over 99 degrees and today it said code (OH) and it wasn't over heated can anyone help?