Method for regulating the combustion air ratio of the burner for a heater for generating heat, having an ionisation sensor which delivers an ionising signal representing current flowing, as a result of an applied voltage, between the burner and an ionisation electrode provided in the region of the flames of the burner, having a fan for conveying the air combustion gas mixture, having a gas valve for supplying combustion gas and having a control device for carrying out the method, having the cyclical method steps a) identifying the current heat requirement to be covered by the heater, b) determining and outputting an air mass flow rate parameter belonging to the identified heat requirement, c) determining a target ionisation signal, on the basis of previously conceived and stored parameters, belonging to the determined air mass flow rate parameter and to the desired target combustion air ratio, d) continuous or quasi-continuous controlling of the gas valve such that the actual ionisation signal is equal to the target ionisation signal, as well as having the method steps carried out at periodic time intervals e) repeating the steps a) to d) for a fixed time period and, after expiry of the time period, reducing the combustion air ratio while simultaneously recording the ionisation signal until the ionisation signal reaches a maximum value, f) determination, plausibility test and correction of the stored parameters and continuance of the method with step a) at a simultaneous new start of the time period, wherein in the case that plausible parameters were not determined in step f), instead of the method steps a) to f), cyclically the method steps g) operating the fan in a previously defined target air mass flow rate parameter and controlling the gas valve with a previously defined valve position, which, together with the target air mass flow rate parameter under previously defined basic conditions, results in a defined target combustion air ratio of greater than 1 h) reducing the air mass flow rate parameter at the simultaneous measurement of the ionisation signal until a maximum value of the ionisation signal is identified, i) determining and storing the air mass flow rate parameter at which the maximum value of the ionisation signal was identified, k) multiplication of the air mass flow rate parameter with a factor which was previously conceived such that a desired combustion air ratio is achieved l) setting the air mass flow rate parameter calculated at k) are carried out. a) identifying the current heat requirement to be covered by the heater, b) determining and outputting an air mass flow rate parameter belonging to the identified heat requirement, c) determining a target ionisation signal, on the basis of previously conceived and stored parameters, belonging to the determined air mass flow rate parameter and to the desired target combustion air ratio, d) continuous or quasi-continuous controlling of the gas valve such that the actual ionisation signal is equal to the target ionisation signal, as well as having the method steps carried out at periodic time intervals e) repeating the steps a) to d) for a fixed time period and, after expiry of the time period, reducing the combustion air ratio while simultaneously recording the ionisation signal until the ionisation signal reaches a maximum value, f) determination, plausibility test and correction of the stored parameters and continuance of the method with step a) at a simultaneous new start of the time period, wherein in the case that plausible parameters were not determined in step f), instead of the method steps a) to f), cyclically the method steps g) operating the fan in a previously defined target air mass flow rate parameter and controlling the gas valve with a previously defined valve position, which, together with the target air mass flow rate parameter under previously defined basic conditions, results in a defined target combustion air ratio of greater than 1 h) reducing the air mass flow rate parameter at the simultaneous measurement of the ionisation signal until a maximum value of the ionisation signal is identified, i) determining and storing the air mass flow rate parameter at which the maximum value of the ionisation signal was identified, k) multiplication of the air mass flow rate parameter with a factor which was previously conceived such that a desired combustion air ratio is achieved l) setting the air mass flow rate parameter calculated at k)