TRVs sense the air temperature around them and regulate the flow of hot water entering the radiators to keep a set temperature in a room. They can help you save money and energy, by allowing you to set lower temperatures in some rooms than in others, and to turn off the heating in rooms that aren't used.

In the majority of cases TRVs can not turn the boiler off when the whole house has reached the right temperature(s). To do that, you will need a room thermostat as well. Radiators in the space containing the room thermostat should not normally have TRVs. But if they do, you should keep the TRVs on their highest possible settings, and set the room thermostat to the required temperature instead.