We were somewhere around Barstow, on the edge of the desert, when the
drugs began to take hold. I remember saying
something like:

Hi all,

How long will PEX pipe last when used in a central heating system?
Googling for this brings up a huge variation, from 10 years, to 100+
years, with all sorts of caveats for different uses (e.g., high
temperature use reduces lifetime to a 1/5th, etc.), so I haven't found
a definitive answer. None of the manufacturers seem to give this
information either.

In truth, nobody really knows. All the manufacturers have been doing is
basing estimates on accelerated testing. There are many twenty year old
installations going strong with no sign of deterioration and many, many
more fifteen and ten year old ones, so we wait and see. I've come across
quite a few ten+ year old ones that seem in fine condition.

Rehau have been making it for 30odd years and they are confident enough
to offer a 25 year warranty, so it's fairly safe, I'd say.

Of greater concern is quality control - a couple of years ago a certain
company here was making pex pipe with pinholes in it - you can imagine
the swearing that went on when fully-plumbed houses were pressure
tested. Ironically, one of the selling points of pex is its total
resistance to pinholes that copper is prone to in an acidic water
environment.