I have Alpha CB24/28 boiler. For 2 day we have had no heating, no hot water and indicator neons A and B are flashing on and off alternatively, which means by fault finding instruction leaflet - low pressure. If system pressure is low repressurisation is required. But how to do it. I found under the boiler taps and valves. One is named as cold water inlet. Is that the right one? I already opened it but I could not hear any sound of water. Please help me, it is quite cold inside.