Thermostatic radiator valves control the temperature of an individual radiator, meaning each room in your house can be kept at the desired temperature, rather than being controlled by one main thermostat. The valve is controlled by a temperature-sensitive substance, usually wax or gas, that opens or closes the valve, depending on the temperature of the room, thus controlling the flow of hot water into the radiator. Fitting thermostatic radiator valves in your home can reduce energy bills because you do not need to heat the entire house --- just the room that you are using.
Turn off the boiler and allow all radiators to cool down completely before starting work. Place old towels or sheets under the radiator you will be working on.
Drain down or plug the system to block the flow of water to the radiator.
Using an adjustable wrench, unscrew the old valve fitting from the radiator and discard it.
Measure the new thermostatic radiator valve and, using the hacksaw, cut the vertical pipe that comes up out of the floor to the required length to ensure that the new valve, when connected, will be in the correct position to be attached to the radiator. Lightly sand the edges of the cut end of the pipe to remove any rough bits of copper to help ensure the valve is watertight when fitted.
Fit the new valve to the pipe by placing the connecting nut on to the pipe, followed by the small brass ring, known as an olive, that should be supplied with your valve. Place the valve over the top of the pipe and screw the connecting nut up onto it, ensuring it is tightened sufficiently.
Connect the other end of the valve to the radiator using the supplied fitting.
Refill the system, turn on the boiler and check for leaks.
Wear old clothes because even though the system will be drained, there is still a chance that dirty water will leak from the radiator. Do not over-tighten the connector for the new valve because this can damage the thread.