There is, of course, a minus in comparison with the above scheme, namely the uneven heating of the room. Yes, and difficult, if not impossible, in a single room to adjust the temperature. Cold water comes from the boiler. To slightly eradicate the minus of the system, you need to connect the thermostat to all radiators and include the circular pump in one line. He rather quickly pumps the carrier through the pipes, which allows him not to cool, which does not give a strong difference in temperature in the rooms.