As for MTBF and durability. I had our central heating serviced today. When I looked at the service report, I happened to notice under pump type 'Grundfos XXXXX' (don't remember the type) and under 'year of installment' 1988.
This baby has been working our central heating for 16 years now. I remembered the thread, descended to my basement. This baby is really quiet. I can put it on 3 pump levels (ranging from 700 to 3000 l/h), the loudest of which is the only one audible in a quiet basement (the only piece of equipment working at the time down there was the pump).... Putting my ear next to it (+/- 5cm) gave me a very slight hum on the other 2 pump levels, barely noticable at 5cm and not even noticable at 1m
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