Worcester 24i combi boiler - can't get hot water without central heating?

My boiler works perfectly when it comes to the central heating, however the only time I can get hot water is when the heating is on. Not a problem during the winter but will turn into a pain come the summer. Turning on the hot water tap should provide hot water without the need for central heating but the boiler just doesn't fire up. I've tried different settings but none of them work. Any help would be much appreciated.