Method for operating a gas burner appliance, wherein said gas burner appliance comprises a gas burner for combusting a gas/air mixture, said gas burner appliance further comprises a primary heat exchanger for heating service water by the combustion of said gas/air mixture, and a secondary heat exchanger for heating domestic water using the heated service water, wherein in a first operation mode or winter operation mode of the gas burner appliance the heated service water is provided to a heating system and/or to the secondary heat exchanger, wherein in a second operation mode or summer operation mode of the gas burner appliance the heated service water is only provided to the secondary heat exchanger, during burner-on phases caused by a heat demand of the gas burner the gas/air mixture having a defined mixing ratio of gas and air is provided to the gas burner, during burner-on phases caused by a heat demand of the gas burner the defined mixing ratio of gas and air of the gas/air mixture can be controlled and/or calibrated on basis of a signal provided by an electrical or electronic sensor, wherein in the second operation mode or summer operation mode of the gas burner appliance the calibration of the defined mixing ratio of gas and air of the gas/air mixture is initiated in such a way that a value being representative of a number of starts and/or of an operating time of the gas burner is monitored, a temperature being representative of the temperature of the gas burner is monitored, if the value being representative of the number of gas burner starts and/or of the operating time reaches or crosses a first threshold, and if further the temperature being representative of the gas burner temperature reaches or falls below or is below a second threshold, then the gas burner is started without presence of a heat demand to calibrate the defined mixing ratio of gas and air of the gas/air mixture. said gas burner appliance comprises a gas burner for combusting a gas/air mixture, said gas burner appliance further comprises a primary heat exchanger for heating service water by the combustion of said gas/air mixture, and a secondary heat exchanger for heating domestic water using the heated service water, wherein in a first operation mode or winter operation mode of the gas burner appliance the heated service water is provided to a heating system and/or to the secondary heat exchanger, wherein in a second operation mode or summer operation mode of the gas burner appliance the heated service water is only provided to the secondary heat exchanger, during burner-on phases caused by a heat demand of the gas burner the gas/air mixture having a defined mixing ratio of gas and air is provided to the gas burner, during burner-on phases caused by a heat demand of the gas burner the defined mixing ratio of gas and air of the gas/air mixture can be controlled and/or calibrated on basis of a signal provided by an electrical or electronic sensor, wherein in the second operation mode or summer operation mode of the gas burner appliance the calibration of the defined mixing ratio of gas and air of the gas/air mixture is initiated in such a way that a value being representative of a number of starts and/or of an operating time of the gas burner is monitored, a temperature being representative of the temperature of the gas burner is monitored, if the value being representative of the number of gas burner starts and/or of the operating time reaches or crosses a first threshold, and if further the temperature being representative of the gas burner temperature reaches or falls below or is below a second threshold, then the gas burner is started without presence of a heat demand to calibrate the defined mixing ratio of gas and air of the gas/air mixture. wherein in a first operation mode or winter operation mode of the gas burner appliance the heated service water is provided to a heating system and/or to the secondary heat exchanger, wherein in a second operation mode or summer operation mode of the gas burner appliance the heated service water is only provided to the secondary heat exchanger, a value being representative of a number of starts and/or of an operating time of the gas burner is monitored, a temperature being representative of the temperature of the gas burner is monitored, if the value being representative of the number of gas burner starts and/or of the operating time reaches or crosses a first threshold, and if further the temperature being representative of the gas burner temperature reaches or falls below or is below a second threshold, then the gas burner is started without presence of a heat demand to calibrate the defined mixing ratio of gas and air of the gas/air mixture.