I hope this is not too stupid a question. I have a heating system in my apartment in which there is a central boiler in the kitchen and the usual radiators around the apartment, they are connected by gold colored pipes along the walls. Both the boiler and each radiator have a dial going from 0 to 5 (including the snowflake). My question concerns the dials. Are the dials on the individual radiators thermostats? If so, should they generally be at the same number? And then what about the dial on the boiler? Is that also a thermostat? But why should there be two? And if not, what is it doing? I have just been leaving the individual radiators around 2 and turning the boiler on and off as I come and go. What is the most economical way to heat the apartment using this system?