A thermostatic radiator valve, commonly known as a TRV, automatically controls the temperature of a room by regulating the flow of hot water to the radiator.
Once the temperature has been set, by turning the valve handle to the required setting the TRV keeps the room temperature at the desired level. The actuating device within the main body of the valve, which is made up of a wax, expands or contracts, subsequently opening or closing the valve and thereby regulates and controls the flow of hot water through the radiator.
A TRV should not be fitted to a radiator where it is in the same room as the main house thermostat, as this will lead to inaccurate overall house temperature control.