Method for operating a gas burner

In a modulating gas burner, the mixing ratio of a gas/air mixture is controlled over a modulation range of the gas burner by a pneumatic controller. During burner on phases, the combustion quality is monitored via a combustion quality sensor. The combustion quality is used to detect tolerances of the pneumatic controller and/or a potentially changing behavior of the pneumatic controller by checking if the combustion quality is inside or outside a defined combustion quality range. When the combustion quality is inside the defined combustion quality range, the mixing ratio of gas and air of the gas/air mixture is not changed. When the combustion quality is outside the defined combustion quality range, the mixing ratio of gas and air of the gas/air mixture is changed by adjusting a gas throttle to compensate for tolerances of the pneumatic controller and/or for a potentially changing behavior of the pneumatic controller.