Before removing a radiator, switch off the heating system and allow enough time for the water to cool down. Have a radiator bleed key (fig 1), plenty of old towels/absorbent cloths and a container/tray for water collection to hand. The water and sludge that can come out of a radiator can stain and ruin floors and carpets so planning ahead is highly recommended.

Fig 1 - Radiator air bleed key

Close both radiator valves at each end of the radiator, one valve (fig 2) will be a control valve which can be closed by turning it clockwise, the other (fig 3) will have a plastic cap which should be removed, then the valve can be closed by turning it clockwise using an adjustable spanner (fig 4). Count how many turns it takes to close so when the radiator is refitted the valve will be open in the same position, (this valve controls water flow through the radiator). 

Fig 2 - Radiator control valve

Fig 3 - Radiator valve with cap removed

Fig 4 - Adjustable spanner

When you are ready to loosen the radiator nut(s) hold the valve in position with another pair of gland pliers (water pump pliers, fig 5) to minimize any strain on the pipework.
 

Fig - 5 Gland / Waterpump pliers

To loosen the radiator nut use a pair of gland pliers (water pump pliers) but don’t loosen it fully, just give one a few turns until water starts to seep out, this can be collected in your tray/container, when the tray/container is full, tighten the nut and empty the tray/container, continue doing this until no more water comes out from the radiator. Now you can loosen both radiator nuts and close the bleed valve.

You may need help lifting the radiator off its fixing brackets, the valves will probably need prising slightly away from the radiator so it can be lifted clear, remember the bottom of the radiator will still contain water and sludge. So as you lift the radiator have a tray/container nearby then tip the radiator slightly to pour the water and sludge out. If you need to store the radiator for any length of time turn it upside down to reduce the chance of any water/sludge coming out and staining floors or carpet.

If you find that the top half of a radiator is not as hot as the bottom, the cause is most likely to be trapped air in the heating system. This can be easily remedied by bleeding the air from the radiator.

First of all, turn off the central heating system, you will need a radiator air bleeding key, which are available at  DIY stores such as B & Q, Focus, etc and an old towel or absorbent cloth. Locate the air bleed valve at the top end of the radiator and hold the towel / cloth just beneath it.

Radiator air bleed key

Radiator air bleed valve

SAFETY POINT – Any water that comes out of the bleed valve may be very hot, so take care to avoid being scalded.

Using the key turn the valve anticlockwise just enough to release the trapped air ( a low hiss can usually be heard ) when water starts to dribble out of the valve close it tightly and wipe away any drips or runs of water from the radiator.

Switch the heating system on and check the radiator. If the radiator still feels cooler at the top repeat the procedure.