Grundfos pumps are installed in hot water systems to function as a recirculation device for the water. When operating correctly the pump keeps hot water moving through the system constantly to ensure that heated water is available whenever you turn on a hot water faucet. This will prevent cooler water from being dispersed as the hotter water reaches your faucets. When air is in the system, the pump loses its efficiency. Venting a Grundfos pump removes the air that can accumulate over time, restoring the pump to efficient use.
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.