Radiator bleeding purges air that has accidentally gotten into the radiator's coils. All radiators must be bled on a regular basis, as the heating and cooling of water naturally releases air bubbles. You can try radiator bleeding if your heater seems to be functioning poorly or not heating as well as it did before.

A radiator works by heating water in a series of coils that effectively warms the air that comes in contact with the metal surface. When air gets in the radiator, it rises to the top and displaces some of the water. Air doesn't conduct heat nearly as efficiently as water, therefore it is both costly and wasteful to run your radiator with air trapped inside.

Experts on home maintenance and energy efficiency recommend radiator bleeding regularly at least twice a year. During the winter season when you use your radiator daily, or have to refill it with water, you may want to bleed your radiator more often. To evaluate whether there is air mixed with water in the radiator, turn on it on for a little while. Carefully use your hand to sense the temperature at the bottom third of the radiator. Compare this to the temperature on the very top of the heater. If there is a wide divergence, you should bleed the radiator.

The procedure for radiator bleeding is simple and safe. All radiators come with a notched fork, called a bleed key. There should also be a protrusion near the top of the radiator, on one side, called the bleed valve. Have ready an old rag, or even a small bowl, if you do not want water dripping on the floor. Fit the bleed key into the bleed valve and carefully turn it counterclockwise only a tiny bit, usually just a 1/4 or 1/2 turn. The air will start escaping with a hissing sound similar to a bicycle tire. When water begins to dribble out, all the air is purged, and you can gently return the bleed valve to its previous position.

If radiator bleeding does not seem to improve the performance of your heater, especially if several radiators in your home are malfunctioning, there may be another problem. A professional radiator inspector can detect whether sludge in the water is gumming up its circulation, or a mechanical component needs replacing. However, radiator bleeding almost always solves the problem.