water pressure gauge wont move up anymore?

I have a Ferroli F30 and in the past, when the pressure bar has dropped to below 1, i've been able to refill it myself by opening the taps connected to the hose underneath. This time though nothing is happening. There is a normal size tap which turns fine but the smaller valve like tap can just be spun round and even when i tightened the screw in it, still nothing happens, i cant even hear the hissing noise so i know nothing is happening. Any ideas?