Whilst the 552 is very reliable, the are about 30% less efficient than the current boiler models.
Efficiency of a boiler may be a quote of what a brand spankng new boiler costs to run annually. Factor in repair costs i.e. cost of high tec parts, labour charges etc to maintain those sky high effiency figures against a clockwork boiler that essentially has two or three main components that rarely breakdown.
95% effiency figure quotes may not be that elevated me thinks.