TRVs (thermostatic radiator valves)
A thermostatic radiator valve (TRV) is a self-regulating valve fitted to a radiator, this controls the temperature of a room by changing the flow of hot water to the radiator.
The classic TRV contains a plug, typically made of wax (forming a wax motor), which expands or contracts with the surrounding temperature. This plug is connected to a pin which in turn is connected to a valve. The valve gradually closes as the temperature of the surrounding area increases, limiting the amount of hot water entering the radiator. waxs plugs are not very accurate, so we install valves with liquid sensors, trvs react much quicker to changes in room temperature and are generally more accurate.
As the valve works by sensing the temperature of the air surrounding it, it is important to ensure that it is not covered by material (such as curtains). The replacement of a manual heating control with a TRV has been estimated to save on your heating bills by up to 17% a year.