fixmyplumbing

If your radiator is cold at the top and hot at the bottom it means there is air trapped inside.

Most radiators have a standard sized key, take this along with a cloth to the radiator if you don’t have a key you can buy one here.  

Place the cloth behind the radiator to protect the wall put the key  on the bleed point give it a gentle turn anti clockwise until you hear air coming out. Stop turning as soon as you hear the hiss of the air leaving the key on the bleed point.  When water starts coming out turn the key clockwise to reseal the bleed point.  Remember the bleed point only needs to be turned until it is just tightened up.   Its only made of brass so turning it hard will snap it off in the radiator causing more trouble.

There are also kits available that collect any water that spills from the radiator when you bleed it. They are available here.

Remember to check the pressure on the boiler when you are finished bleeding radiators if you have a sealed central heating system.