LZB

I have a Balboa 3seater VS series spa. it was in economy mode and it would only reach 104 snd then cool down when in use. I switched it on and to standard mode and it heated to 104 and stayed at 104-103 while in use. I then turned it off. It started on its own next day, and kept running till it reached 137, it would not turn off when I tried to turn it off. Had to pull power switch. Anyone have a clue what could be wrong????