Central heating radiators require occasional bleeding to remove air from the system. If not fully bled they may not be getting as hot as they should. Usually the top of the radiator is colder than the bottom. In extreme cases radiators will not heat up at all, usually following a full draining of the system.
To bleed your radiators you will need to check a type of bleeding valve that you have installed on your radiators. The most popular type is a small square bleeding valve that will require a bleeding key to operate it.
Bleeding key can be purchased in most hardware stores and some convenience stores. They are small brass or metal keys and look as on the picture below.
There are some bleed valves that can be bled using a flat screwdriver as well as a bleeding key. It is always easier to bleed radiators using a bleeding key. Please be aware that there are automatic bleeding valves on the market that do not require to be bled manually. An example of automatic bleeding valve can be seen on the picture below.
To bleed your radiators you will need to do following:
1. Make sure your boiler is off by turning your central heating thermostat off
2. Get a cloth or kitchen towel to catch water when bleeding radiators. Be careful as on systems that are not well maintained system water may be contaminated with products of oxidation and it can stain carpets.
3. Make sure that valves on the radiator are in on position. On thermostatic valves it is fully anticlockwise position.
4. Undo bleeding valve using either radiator bleeding key or flat screwdriver. To do that, turn the valve anticlockwise by 2 – 3 turns. If you turn it too many times anticlockwise you run a risk of valve shaft coming out. It is not fun trying to put it back with water spilling all over the place!
5. With the valve open (2 – 3 turns!) wait for the air to vent. When water starts to drip turn the valve off by turning the valve fully clockwise.
6. If you have a sealed system remember to top it up using a filling loop as pressure may drop if there had been to much air in the central heating system. If your boiler has a pressure gauge then most likely you have a sealed system. Pressure gauge looks like on the picture below. If you do not know how to top up your system read an article on pressurising your boiler .