Am about to replace boiler and would welcome recommendations. Current boiler which is 25 years + old is an Ideal Vulcan RS 55 but think a slightly higher rating would be better (think it is 55000 btu). Want a heat only condensing boiler and an unvented indirect hot water cylinder. Am considering the Worcester Greenstar 18RI and the Keston 150L or Santon 150 L cylinder. Anyone have any recommendations as to what we should go for