A printer comprising a printing fluid circuit having at least one printing fluid supplier, an air pressurization system to build up air pressure inside the at least one printing fluid supplier, and a controller is provided, wherein the air pressurization system is fluidly connected to the at least one printing fluid supplier. The controller is to determine the air pressure which has been built up in the at least one printing fluid supplier by the air pressurization system, and to determine a degradation of the air pressurization system depending on the air pressure which has been built up in the at least one printing fluid supplier by the air pressurization system.