In article , Andrew
Gabriel writes
I was servicing my Keston Celcius 25 yesterday.

Over the years, I have noticed slight rust staining on the
bottom of the inside of the cover along the metalwork seam.

Thanks Andy, I've not noticed this on mine but will keep a look out. I
wonder if it depends on the flue configuration, natural convection meaning
that some (mine) don't see this but others do. If it helps, mine has a short
neutrally ventilated inlet with a v long vertical outlet.
--
fred