British Gas 532/i Gas Combi Boiler?

Hi Please could you help? I also have British Gas combi Condensing boiler RD532i. Installed 2006. Never given me any trouble. But just recently when running the hot water after 3-4 mins the boiler just seems to switch off and the water temperature drops until it is cold. If I leave it a while and try again, the water heats up ok; but then again after a few mins it cuts off and runs cold.
Does anyone know what the issue may be; like temp sensor or pressure switch that may be causing this sort of issue ?
There is no error cod showing !!