Bran new ideal auto air vent 176457. The automatic air vent is a safety device within the central heating unit. They work by using buoyancy to release built up air. As water circulates through the heating/cooling system, a float within the automatic air vent opens or closes depending on the water level. If the system is full of water, the float will be pushed to the top and the vent will be closed until the water level drops. These parts are Non Branded Compatible/Alternative components that can be used as alternatives to branded parts, as such they will not come in boiler manufacturers packaging.