A method for closed-loop control of a gas mixture (9, 108) formed from a gas (2, 105) and a combustion gas (1, 103) in a combustion-gas-operated heating unit, wherein the gas mixture is produced by providing an amount of gas via a first control element (4, 107) and an amount of combustion gas via a second control element (3, 102) and mixing said amounts, wherein a microthermal gas sensor (8, 106) which detects at least one material property of the gas (2, 105) is exposed to the gas and transmits a sensor signal, which is dependent on the respective gas, to a control device (11, 113), a microthermal combustion gas sensor (6, 104) which detects at least one material property of the combustion gas (9, 108) is exposed to the combustion gas and transmits a sensor signal, which is dependent on the respective combustion gas, to the control unit (11, 113), a microthermal gas mixture sensor (10, 107, 109) which detects at least one material property of the gas mixture (9, 108) is exposed to the gas mixture and continuously transmits a sensor signal, which is dependent on the respective gas mixture, to the control unit (11, 113), wherein the detected sensor signals of the combustion gas sensor (6, 104) are compared by the control unit (11, 113) with laboratory-measured comparison values stored in a value table in the control unit (11, 113), and a combustion gas composition and a target mixing ratio of the gas mixture (9, 108) of combustion gas and gas are determined therefrom, wherein the target mixing ratio is present at a target value of the sensor signal of the gas mixture sensor (10, 106, 109), and wherein the control unit (11, 113) compares the detected sensor signal of the gas mixture sensor (10, 106, 109) with the target value of the sensor signal of the gas mixture sensor (10, 107, 109) and, in the event of a deviation of the detected sensor signal from the target value of the sensor signal of the gas mixture sensor (10, 107, 109), activates at least one of the first and second control elements depending on the detected sensor signals of the gas sensor (8, 106) and of the combustion gas sensor (6, 104) and thereby adjusts the gas mixture (9, 108) by increasing or decreasing the amount of gas and/or increasing or decreasing the amount of combustion gas until the target value of the sensor signal of the gas mixture sensor (10, 107, 109) is reached, characterized in that the target value of the sensor signal of the gas mixture sensor (10, 107, 109) is adjusted by the control unit (11, 113) depending on a composition of the gas or of the combustion gas, and wherein adjusting the target value of the sensor signal of the gas mixture sensor (10, 107, 109) is carried out by a calibration process. a microthermal gas sensor (8, 106) which detects at least one material property of the gas (2, 105) is exposed to the gas and transmits a sensor signal, which is dependent on the respective gas, to a control device (11, 113), a microthermal combustion gas sensor (6, 104) which detects at least one material property of the combustion gas (9, 108) is exposed to the combustion gas and transmits a sensor signal, which is dependent on the respective combustion gas, to the control unit (11, 113), a microthermal gas mixture sensor (10, 107, 109) which detects at least one material property of the gas mixture (9, 108) is exposed to the gas mixture and continuously transmits a sensor signal, which is dependent on the respective gas mixture, to the control unit (11, 113), wherein the detected sensor signals of the combustion gas sensor (6, 104) are compared by the control unit (11, 113) with laboratory-measured comparison values stored in a value table in the control unit (11, 113), and a combustion gas composition and a target mixing ratio of the gas mixture (9, 108) of combustion gas and gas are determined therefrom, wherein the target mixing ratio is present at a target value of the sensor signal of the gas mixture sensor (10, 106, 109), and wherein the control unit (11, 113) compares the detected sensor signal of the gas mixture sensor (10, 106, 109) with the target value of the sensor signal of the gas mixture sensor (10, 107, 109) and, in the event of a deviation of the detected sensor signal from the target value of the sensor signal of the gas mixture sensor (10, 107, 109), activates at least one of the first and second control elements depending on the detected sensor signals of the gas sensor (8, 106) and of the combustion gas sensor (6, 104) and thereby adjusts the gas mixture (9, 108) by increasing or decreasing the amount of gas and/or increasing or decreasing the amount of combustion gas until the target value of the sensor signal of the gas mixture sensor (10, 107, 109) is reached, characterized in that the target value of the sensor signal of the gas mixture sensor (10, 107, 109) is adjusted by the control unit (11, 113) depending on a composition of the gas or of the combustion gas, and wherein adjusting the target value of the sensor signal of the gas mixture sensor (10, 107, 109) is carried out by a calibration process.