Abstract: A spa is maintained at a ready-to-use temperature by a daily heating cycle that is initiated by a filter cycle clock, which traditionally has been used only for programming the circulation of the spa water through a filter. Once a daily heating cycle has been initiated, it normally concludes only when the temperature of the spa water reaches a desired temperature that the user has preset into a thermostat. However, for safety the heating cycle is terminated immediately in the event the heater temperature becomes excessive, since this event could result from lack of water or inadequate circulation.