You control the temperature in your living room with the room thermostat. The radiator in the living room should always be fully open. The radiator in the bathroom and in the bedroom can be set using the thermostat knob on the radiator.

Are you going away for a longer period of time?
Then set your heating to a lower setting, around 15 ºC is a good option, so it doesn't cool down too much. That way you won't burden the environment unnecessarily.