On the side of the radiator opposite the flow control valve and bottom piping connections, you will find the air bleed valve. After opening the system fill valve, open the bleed valve by turning the central screw counter-clockwise with a small wrench, flat head screwdriver, or radiator key. You will soon begin to hear and feel air rushing out of the radiator. Be prepared to shut the air bleed valve quickly by turning the screw clockwise. Once the air has escaped, water will begin to flow through escape hole.