hi all a friend of mine is recently after buying a house in co. cork it has gas heating and from what i have been told its an A rated house my only concern was when he told me there is no other way of heating hot water other than the gas heating so if for whatever reason gas goes he has no way of getting hot water i was under the impression that an immersion had to be installed as back up but would just like to know what is the requirement if any of a back up