The invention relates to the control of burners, e.g., for boilers or furnaces and has for its objective to provide means whereby the combustion conditions existing at a burner are initially governed by pre-determined conditions which conditions can be automatically maintained or improved during the operation of the burner. This objective is met by the provision of control means for the reactant flow ratio for at least one burner comprising separate valve means for the control of flow of fuel and of air to a burner, a variator associated with each valve for the setting of the position thereof, sensing means associated with each valve for the sensing of the position thereof, a memory device for holding data pertaining to the characteristics of the control means, a computing device for controlling the variators to determine the positions of the valves in accordance with data in the memory device and detector means associated with the or each burner for the detection of a pre-determined parameter of combustion, both said sensing and detector means being connected to the memory device and whereby the data in the memory device can be continuously up-dated and whereby the computing means can optimize the performance of the control means on the basis of the feed-back of information from the said detector means and sensing means.