In article , YAPH
writes

I take it that was the plate heat exchanger (sort of brick-like metal
block with 4 holes or pipes on it)?

No, it was a metal cylinder (like a drinks can on steroids)

Silt = black gritty/flakey crud?

Yes, larger grains than sand, black, quite loose, not adhering to
anything at all.

--
(\__/)
(='.'=) Bunny says Windows 7 is Vi$ta reloaded.
(")_(") http://imgs.xkcd.com/comics/windows_7.png