You can adjust the maximum achievable set temperature for the portable control unit so that the maximum temperature the spa can reach is restricted to 38, 40 or 42 deg C.
Hold down the HEAT and JETS buttons together for a few seconds until the display shows F0, F1, or F2.
Use the "+" or "-" buttons to adjust between F0/F1/F2
After the setting is chosen, wait until the number on the display stops flashing, then press any key to exit
F0 = max setting temperature 40°C / 104°F
F1 = max setting temperature 38°C / 100°F
F2 = max setting temperature 42°C / 108°F