Page "Thermostatic radiator valve" Paragraph 12

Note that a TRV cannot manage room temperature without a thermostat somewhere in the system to signal the heating source to kick in and produce hot water or steam.

For example, in a three-bedroom apartment with a living and dining area, there has to be a thermostat in the apartment to signal the boiler to produce hot water.

If the thermostat for the apartment is located in say, the living area, then any TRV's installed on radiators in the bedrooms can manage temperatures in those rooms, provided the thermostat in the living room is calling for heat.

So if we wish to turn down the thermostat in the living room when we go to bed then the bedroom radiators will only get heat if the living room temperature is above the temperature setpoint in the living room.