Please if anyone can help,I have cold water coming out my cold water tap, hot water out the hot water tap. But after a few minuets,the hot water stops and the boiler stops as well. The cold water continues from the cold water tap. After waiting for twenty minuets or so,the hot water starts working again for a few minuets. This happened about three months ago,after a few days everything started to work fine and now its happened again its doing my head in. If I turn the hot water tap on the boiler fires up and then the hot water slowly gets less and less then nothing which in turn shuts the boiler of? Please help and thanks in advance.