On Thu, 25 Jan 2018 15:30:52 +0000 (GMT), Tim+
wrote:

snip

So, it's clearly not the rubber swelling as I imagined but a build
up of either corrosion of the fitting itself or deposition of
crud in the pipework perhaps exacerbated by small internal bore
of the connectors. (About 6mm).

It all seems strange to me as the last system I worked on was my Mums
and that's mostly an ex gravity system and the pipe sizes are huge!
;-)

Anyhow, as this is the second time I've seen this happen with
these flexible hoses in CH systems I think that it's a strong
indication never to use them.

Or anything that substantially reduces or restricts the flow,
especially where it's not easy to access / service.

The radiator is now toasty and warm for the first time in years.

Excellent.

A very satisfying hour's work.

It's lovely when a plan comes together eh. ;-)

Cheers, T i m