On the contrary Mehan. 700,000 heat exchangers have been made for this boiler with 0% failure. Anyone who looks at the insides of one can see how inherently reliable it is and also how efficient it is. They are not clogged by sludge, can be easily descaled (although I have only heard of ONE that has scaled up in the Cheltenham area, and that was several years ago). We were shown a thermal image of a heat exchanger in operation, and it is very impressive; pity they won't release the video fro commercial reasons.
Granted by the standards of some manufactures these are relatively low figures, BUT remember these boilers are not just fitted in the Uk and they do not have many parts. The heat exchanger is pretty much all there is to it. Remember 0% IS 0%.
The thing that many people seem to ignore is that plate heat exchanger technology has hardly changed over recent years,