Abstract: A thermostat controlled circuit for a bias heater located adjacent the thermostat connected to a source of alternating electrical power. The control circuit has a manually operated switch for providing a temperature level signal. A triac having a gate terminal and first and second terminals connected in series with the AC power source and the bias heater is provided. A transistor circuit controls the operation of the triac and is connected to the gate of the triac to provide a signal for turning on the triac periodically. The microprocessor supplies an enable signal to the transistor circuit at predetermined time intervals to cause the transistor circuit to activate the triac. The triac turns off at the next zero crossing of the AC line current after the microprocessor has removed the enable signal from the transistor circuit. The point in time of turning on the triac may be synchronous or asynchronous with the AC line current.