Abstract: A flame atmosphere analyzer is described, for operation with combustible gases, including a tube in which an intake and air and gas mixing chamber is formed, a first gas supply nozzle and means for supplying primary combustion air opening into said intake chamber, and a flame burner in fluid communication with the intake and mixing chamber for supplying an air and gas mixture, formed in the chamber, to the burner. The analyzer includes a second gas supply nozzle, which is slidably guided in the tube, and an actuator provided on the tube and operable from outside the tube, for moving the second nozzle between an inoperative first position, in which the gas is supplied through the first nozzle, and an operational second position, in which the gas is supplied through the second nozzle, the first nozzle having no effect on the supply of the gas in the second position.