If I remember correctly, the theory was that the cost and effort of actually having to raise the boiler anyway would make the decision to replace it more economical, and make a replacement worth considering.
This was years ago, and I can't recall who it was that made the speculation.
Thanks for the clarification. If anything, 476's boiler having been idle this long (almost 7 years?) should put it with considerably less time than the other two by now. None of the 470's have been down this long before.
^^ak