We have investigated the sensing properties of Al2O3-doped ZnO for combustion control in lean-burn conditions. Planar-type sensing elements made of heater, electrode and sensing layer were formed on an alumina substrate using a screen-printing technique. Our exhaust-gas sensor exhibits significant resistance changes even under lean conditions, apparently due to the simultaneous functioning of bulk and surface conduction mechanisms. Utilizing the sensor for the feedback control of a domestic boiler, we have demonstrated that the system can be successfully operated at the best combustion conditions.