Method for operating a gas burner

Method for operating a gas burner (10), wherein during burner-on phases a defined gas/air mixture having a defined mixing ratio of gas and air is provided to a burner chamber (11) of the gas burner (10) for combusting the defined gas/air mixture within the burner chamber (11), wherein the defined gas/air mixture is provided by a mixing device (23) mixing an air flow provided by an air duct (15) with a gas flow provided by a gas duct (16). During burner-on phases the defined mixing ratio of gas and air of the defined gas/air mixture can be calibrated to different gas qualities on basis of a signal provided by an ionization sensor (13) positioned downstream of the mixing device (23) within the burner chamber (11). For the calibration of the gas/air mixture the gas/air mixture is made richer by increasing the gas amount of the gas/air mixture relative to the air amount of the same until a flattening or a maximum of the signal provided by the ionization sensor (13) is detected, whereby the further calibration of the gas/air mixture depends on if either a flattening or a maximum of the signal provided by the ionization sensor (13) is detected.