On 04/03/2021 16:12, Another John wrote:
I've just been in the loft, and thought that while I was there I'd look
into the cold water tank (incredibly corroded parts, the tank itself
being PVC, but it all works) and the CH feed/overflow tank.

Soft water region? Mine the limescale builds up on the regular splashes.

The CH tank has a skin on it that must be at an inch deep - browny,
almost solid gunge on top, pitch black underneath where it's in contact
with the surface of the water. Looks absolutely ghastly.

Your problem will be if you ever need to drain down the CH system in a
hurry. Thick brown gunge and microbore piping do not get on at all well.

Is it organic looking gunge or precipitated copper/iron hydroxide rust?

I'm slightly surprised that it floats.

I am intending to get the CH boiler serviced this Spring/Summer. (I
rarely get it serviced, on the old adage "if it ain't broke don't fix
it". However it's almost 6 years since it was last looked at, so I think
it's time.)

So: when getting the boiler serviced, should I get the tank looked at as
well?


Note 1: I took care not to stir it up after I'd discovered the gunge.
However I'd guess that part of the reason this skin has formed is that
the system doesn't access the tank much, if at all.

Note 2: I have both cold water and CH tanks covered with thick insulated
boards, to prevent freezing -- was that a bad idea?

That it is covered means it isn't due to a dead bird or bat rotting away
in the tank and providing nutrients for the brown gunge.

Note 3: this is a patchwork system (like most, I'd guess): rads and
pipework (microbore) fitted at least 35 years ago; new boiler and
controls and minor mods in 2008; and the boiler, which is a Gloworm
Flexicom HX, had a new heat exchanger fitted in 2015. Nothing since then.

Thanks in anticipation, for any views!

Was there any inhibitor in the system?

--
Regards,
Martin Brown