A lightweight, compact soldering and desoldering instrument including a temperature sensor at the soldering tip. The sensor is of a type to provide a large change of resistance with a small change of temperature thereby to unbalance an electric bridge to create an error signal which in turn turns on or off the heating element of the soldering instrument. The entire electric control circuit is carried on a printed circuit board slidably disposed in the handle of the instrument and provides a closed loop temperature control. A closed tool holder is provided for maintaining the soldering instrument at its operating temperature when it is not in use thereby to extend the life of the soldering tip and to minimize the heating current. The control circuit is also provided with a special fuse which responds both to a thermal overload and an electrical overload to disconnect the current supply. The temperature of the soldering tip may be set by a control potentiometer in the handle of the instrument in accordance with different requirements.