When you finish hot tubbing, turn the heater to the "off" position. Otherwise after five days you discover this heater setting when you go out to turn on the hot tub. And since you remembered to reset the flow valves the last time you hot tubbed, now your pool is steaming warm in the cold February night air. And it probably cost you many tens of dollars to run the pool heater all week.
Anyone want to come over and swim? Pool's warm.