Heating fluid control system for a building comprising a boiler configured to heat heating fluid and sources of demand configured to use the heating fluid from the boiler, the sources of demand including at least one radiator to be associated, in use, to each of a plurality of zones of the building configured to radiantly heat the respective zone using heat of the heating fluid, the heating fluid control system comprising: at least one radiator valve for each of the plurality of zones, each radiator valve being fluidly connected between a radiator in the respective zone and the boiler and being selectively openable and closable to control the heating fluid that is supplied to the respective radiator from the boiler, each radiator valve being further configured to transmit a radiator demand signal representative of a demand of the respective radiator for the heating fluid; and a controller operatively connected to the boiler and to each of the radiator valves to receive the respective radiator demand signal, the controller being configured to determine, based at least in part on the radiator demand signals for each of the radiator valves, when a demand for heating fluid from the sources of demand of the building is zero and to transmit a boiler deactivation control signal to the boiler when the demand for heating fluid from the sources of demand is determined to be zero, the boiler deactivation control signal being configured to automatically deactivate the boiler when the boiler receives the boiler deactivation signal; characterized in that the heating fluid comprises hot water and the sources of demand further include a domestic hot water fixture, the heating fluid control system further comprising at least one domestic hot water valve fluidly connected between the boiler and the domestic hot water fixture and selectively openable and closable to control the hot water that is supplied to the domestic hot water fixture, and wherein the domestic hot water valve is configured to transmit a domestic hot water demand signal to the controller representative of a demand of the domestic hot water fixture for the hot water, and the controller is configured to use the domestic hot water demand signal to determine when the demand for heating fluid from the sources of demand is zero; and wherein the controller is configured to determine that the demand for heating fluid from the sources of demand is zero only when the radiator demand signal of each of the radiator valves and the domestic hot water demand signal of the domestic hot water valve represent zero demand from the respective source of demand. at least one radiator valve for each of the plurality of zones, each radiator valve being fluidly connected between a radiator in the respective zone and the boiler and being selectively openable and closable to control the heating fluid that is supplied to the respective radiator from the boiler, each radiator valve being further configured to transmit a radiator demand signal representative of a demand of the respective radiator for the heating fluid; and a controller operatively connected to the boiler and to each of the radiator valves to receive the respective radiator demand signal, the controller being configured to determine, based at least in part on the radiator demand signals for each of the radiator valves, when a demand for heating fluid from the sources of demand of the building is zero and to transmit a boiler deactivation control signal to the boiler when the demand for heating fluid from the sources of demand is determined to be zero, the boiler deactivation control signal being configured to automatically deactivate the boiler when the boiler receives the boiler deactivation signal; characterized in that the heating fluid comprises hot water and the sources of demand further include a domestic hot water fixture, the heating fluid control system further comprising at least one domestic hot water valve fluidly connected between the boiler and the domestic hot water fixture and selectively openable and closable to control the hot water that is supplied to the domestic hot water fixture, and wherein the domestic hot water valve is configured to transmit a domestic hot water demand signal to the controller representative of a demand of the domestic hot water fixture for the hot water, and the controller is configured to use the domestic hot water demand signal to determine when the demand for heating fluid from the sources of demand is zero; and wherein the controller is configured to determine that the demand for heating fluid from the sources of demand is zero only when the radiator demand signal of each of the radiator valves and the domestic hot water demand signal of the domestic hot water valve represent zero demand from the respective source of demand.