If your radiator ever feels cold at the top and warm at the bottom then it is more than likely that the problem is being caused by air that has been trapped in your radiator. Luckily, you should be able to fix the situation yourself by bleeding your radiator. Another option for you is to call out a plumbing and heating engineer. However bleeding a radiator is a fairly simple, safe and quick process if it is done the right way. Ultimately it just requires opening a small valve on the top of your radiator to permit any trapped air to escape. Just follow the simple instructions below for a quick and lasting fix:

Prior to bleeding your radiator, it's very important you turn off your central heating at the main controls. It will prevent any more air from entering the heating system. Find the bleed valve; this usually has a small red coloured handle and is located on one side of your radiator when it was bought.

Put a cloth or a small bowl underneath the bleed valve to catch any leaking water. Wrap your hand in a cloth to protect your hand as any water that escapes from your radiator could be very hot. Your radiators should have come with a tiny bleed key (or radiator key). If you can't find the bleed key you should be able to purchase a replacement from your local DIY store.

First you will need to locate the bleed valve, this will be a protrusion at the top of one side of the radiator. To bleed your radiator, place the bleed key onto the valve and carefully turn it anticlockwise (usually a quarter to half a turn should do the trick). The air trapped in your radiator will start escaping with a hissing sound. At this stage you may have to switch on your heating for a short period to keep the pressure up in the system. When you are bleeding your system you also have to keep an eye on your water pressure level. When water begins to dribble out of the valve this is how you know that all the air has been purged from the radiator.

As soon as water starts to dribble out of the valve you will require to tighten the valve back to it's original position. Go to your main control panel and check your water pressure leve. This level has to be set at manufacturers levels. Use a cloth to clean up any spills (at this point be careful as the water could potentially be scalding hot). Do not forget to switch the central heating back on once you've finished bleeding the radiator. Check on your radiator after a couple of hours to ensure the radiator has an even temperature all over it's surface area and that there is no more water leaking out of your bleed valve. Hopefully this will mean that your problem is solved!

Remember, if you're ever in doubt of your DIY abilities, then it is best to call in a plumbing and heating engineer to mend the problem for you.