I have a VAILLANT ecoTEC plus VC 20 CS/1-5 and reach of my radiators has a TRV. I understand that when the TRV is set to 3 and the room reaches a temperature of 20C, the TRV will prevent hot water flowing in to the radiator and instead flow to the next radiator. When all the TRV are closed, I assume the hot water bypasses all radiators and returns to the boiler. The TRV are not connected to the boiler, and I have no thermostat in the house that is connected to the boiler. How then does the boiler know that all the rooms are heated appropriately and that it should stop heating water?