Turn off the heating system to avoid steam burns when venting the pump. Allow the water within the system a few hours to cool before you attempt the venting process. The pressure in the system will remain, forcing out the air as you vent.
Put on a pair of heat resistant work gloves and safety goggles just in case the water still retains some heat, and to prevent the water from splashing onto your hands or into your eyes.
Locate the large vent screw on the top of the pump. The screw will be shaped for use by a flat-head screwdriver.
Take the large flat-head screwdriver and place it into the slot of the venting screw on the pump. Turn the screw counter-clockwise to loosen it in place. You should hear the sound of escaping air as you turn the screw. Wait for the appearance of water around the screw edges to indicate that the air is vented and that the water pressure within the system is attempting to push water through the vent opening.
Tighten the screw back into place by turning it clockwise. Turn the heater back on. When the heat reaches its regular temperature, you can use the hot water faucets normally.