I bought a used hot tub that was working and after having it delivered on first startup it has OH as a code. It is a calspa 2001. the water is cold so i am confused. can anyone help?

OH is for over heat, and is likely due to lack of water flow through the heater, causing the heater housing to overheat (where your over heat sensor is located). Check for proper flow of water, perhaps even the circulation pump to ensure all are adequate