What are bleeders, how do they play their part?

Bleeders are miniature valves sitting at the top of the radiator, that when opened up, allows the air to exit the radiator so that the water can come in.  When a heating system is installed and you find a radiator that’s only half-warm, it’s probably half full of air. When the system is filled up, water has flowed into the distribution system, and then into the radiators. Bleeders are then used to get that air out of the radiator.

Most people will generally bleed their heating systems every year to ensure the rad is full and they get the most energy out of the radiator.  Water is full of dissolved gasses by nature, and it takes several years for all that dissolved gas to come out of the water.

Air should be bled out of the rads for a few reasons. One – it has oxygen in it; oxygen eats metal, especially when wet.  A system full of air circulating with nice warm water will eventually deteriorate the structure of the piping and the radiators making it essential to get all that oxygen out of the system. There is another reason why rads should be bled – if the rad is sized to the room, and it’s only half full of water, you’re only getting half the energy out of that radiator. It’s best to get the air out, fill it up, and be able to capture all that energy.