| 摘要 |
<p>A hot water central heating system has a boiler 1, a circulating pump 4, and a controller 5 which varies the speed of the pump between pre-set maximum and minimum speeds in accordance with the difference in temperature of the water leaving and returning to the boiler as measured by temperature sensors TH1 and TH2 in the supply and return pipes 2 and 3 respectively. The system has conventional high and low thermostat contacts 11 and 12 for controlling the boiler 1, and also has contacts 13 in parallel with the contacts 12 and arranged to open to shut off the boiler when the pump 4 operates at minimum speed. The boiler switches on again if the speed of the pump increases, thereby closing the contacts 13, or if the contacts 12 are closed. <IMAGE></p> |
