John Stumbles wrote:
However if the place is for rental then as others have pointed out you
really need to consider what will happen _when_ the boiler breaks down
(they all do at some time or other). A stored water system (conventional
gravity fed, unvented or thermal store) will allow you the option of
electric backup heating for water, though not for space heating.

It also provides stored hot water in the event of a mains electricity or
water failure. Even if the cylinder hasn't fully reheated, it will be
tepidly warmer than the cold mains. Although rare, extended water and
electricity failures do occur.

Owain