Sometimes there are problems with a central heating system that you can diagnose yourself.
If the top of your radiator is cold and the bottom is warm it probably means that the radiator needs bleeding. If you want to check this take care to not burn your hand on the radiator.
If the radiator is almost full of air, no difference in temperature between the top and bottom of the radiator will be felt, but in these extreme cases, the whole radiator will be cool. This will contrast with the rest of your central heating system where the other radiators will be hot to the touch.
You should only bleed your radiator when there is a problem such as that described above. If there is no problem leave well alone.
How do I bleed a radiator?
The procedure for radiator bleeding is relatively simple and safe. All radiators come with a small tool called a bleed key. There will also be a protrusion near the top of the radiator, on one side, called the bleed valve. You want to open this valve a small amount to allow the air to escape from the top of the radiator whilst not allowing the water to flow out.
If you plan to bleed a radiator in a sealed central heating system you will need to reduce the overall pressure of the entire system (consult your manual), this shouldn’t be a problem if you top up the system afterwards from the main cold water feed.
TAKE CARE when turning the valve. Have an old rag ready to shield your hand and a small bowl to catch any small drops of water which escape. that you do not want water dripping on the floor.
First turn off the heating or you could import more air into the system. 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. You should then remember to turn the heating back on and check that there are no leaks from the radiator valve -- did you tighten it again?
As stated before if the central heating system was a sealed system, check the pressure and top up where necessary by consulting your system manual.
For a quick overview of the whole process look at the following video which uses a radiator key to bleed the radiator.
If your radiator needs a screwdriver to open the bleed valve this quick video will help you to see what to do.
What if the problem remains?
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. This could be more complex than you are able to solve. In this situation you should consider calling in an expert or using the customer help line on your central heating care plan.