Radiator Thermostats (also known as Thermostatic Radio Valves - TRVs) sense the air temperature in the room where the radiator is and control the radiator accordingly. If it is too warm in the room they turn it off; if it is too cold they turn it on.
By allowing you to set different temperatures in different rooms they allow you to save energy and money and improve the comfort of your home.
These devices should not be installed on any radiators in the same room as the main thermostat. If the radiator control is set lower than the wall thermostat, then the boiler will keep working and over-heating the other parts of the house, while the temperature in the room where the thermostat is will stay at the lower temperature set on the radiator thermostat. If there are radiator thermostats in the room where your wall thermostat is, then you should set these to maximum, and control the temperature with the wall thermostat.
Radiator thermostats need a free flow of air to sense the temperature, and so should not be covered or blocked by furniture or curtains, or be near other objects that produce heat, e.g. electric fires, lamps etc.
