The automatic air vent is used as a safety device within a central heating unit. How they work is by using buoyancy to release build compressed up air. As the water begins to flow down the heating or cooling system, a small float within the now automatic air vent gaping open and closed, whilst considering the water level. When the system fills up with water, the small floating device will rise to the top and then the vent will automatically close until the water level lowers. It’s very recommendable that all the parts that you buy are professionally fitted by a fully qualified and serviced engineer; feel free to contact us through our details if you require any help on choosing the right part for your system. We have a vast knowledge of experience on all system parts. Don’t be afraid to phone or email our team.