Airlocks are a major problem in many radiator systems. When new water is added to a central heating system, a certain amount of air also enters the system. The action of the pump also draws out dissolved air from the water while slight leaks also allow air to slowly enter the system. Finally open systems (other than apartments, most systems are open systems) which are supplied with water from a tank small in the attic can cause problems where the tank is allowed to run dry for some reason, allowing air to leak into the system.
As air is lighter than water, it rises to high points in the system, this is especially noticeable within radiators. Air in radiators mean less water in the radiator and so can be detected as points which provide less heat and so are cooler to the touch, When the system is switched on, feel the top and then the bottom of the radiator – if the top is noticeably cooler than the bottom, there is a good likelihood that there is air in the radiator.
In very severe cases, the whole of the radiator may be filled with air so no difference in temperature between the bottom and the top, though the radiator in question will be cooler than the others.
How to bleed a radiator
- If the central heating system is an open type, ensure that the water supply tank for the system in the attic has not run dry
- If the central heating system is a sealed system, check the pressure and, if necessary, top it up as required. This is a bit more complicated so check out here for more advice.
- When the system has heated up, switch it off completely. If you do not switch off the system, particularly the pump, there is a good chance more air will be drawn into the system while you are bleeding.
- A “bleed key” is used to open the bleed valve. The bleed valve can be found at the top at one end of the radiator. A bleed key to fit the valve can be purchased in any good hardware shop.
- Loosely wrap a piece of old cloth around the key to catch any expelled water. If you are careful there should be no need for a pot to catch water, but if it’s your first time, it might be prudent to have one just in case.
- Slowly open the bleed valve by about half a turn anti clockwise. You should hear a hissing sound
- When water starts to dribble out, close the valve. They are generally quite easily damaged so take care not to over tighten.