*URGENT* Hot Water?

The hot water at the house I just moved in runs out very quickly- 5 mins to be exact. I have tried adjusting the hot water boiler to the level "Very Hot", but i am still having problems. The water won't boil constantly and runs out very quickly. I do realise that the boiler is one of the old models, but i don't think that would have anything to do with this problem. Is there anything I can do about this?