Abstract: A pool/spa heater having a temperature control portion which is connectable to an external temperature regulating controller, in which the temperature control portion has at least one primary temperature limiting control switch with a first temperature setpoint, at least one secondary temperature limiting control switch with a second temperature setpoint, a third switch adapted for connection with the external temperature regulating controller, and wherein the second temperature setpoint is higher than a maximum temperature setting on the external temperature regulating controller but lower than the first temperature setpoint. The temperature control portion can further have an on/off switch.