OP he I THINK I'VE FIXED IT.

I went up the loft this morning to take pictures (see below). I took
with me an egg, and even a can of beans: I was sure that the gunge-mat
that had formed would support at least the egg! But in fact it felt like
it would slip through, so I didn't risk it.

Then I thought: well, since I'm here, why not siphon it all out? In
short, that's what I did:

1. Switched off the system.
2. Tied up the ballcock to prevent filling while working.
3. Stuck a cork in the outlet to the CH system (very gently, so as not
to disturb the sediments).
4. Ran a hose to the bath, sucked at it, hastily stopped sucking when
the resistance went -- and off we went.

The gunge was solid, but very squidgy, and so went down the hose no
bother (it did block the bath-plug, when running away, but the
siphon-suction was strong enough to prevent blockage in the hose).

I took a soft brush (from a brushpan set - that size) to clean the ****
off the tanks and ballcock, and ran the sucking hose around to get it
all away. I refilled and siphoned the tank twice, and then finally
filled it a third time. I'll look at it in a week's time.

While I was there I looked again at the cold water tank: the water's
(reasonably) clean, but the ballcock mechanics are very cruddy -- any
suggestion for that? Replace entirely?

Final request for advice (I jolly well hope): I had covered both these
tanks with a solid cover, and insulation. Was this a mistake? Would an
old blanket (or anything else that might protect from severe frost etc,
but allow breathing) have been better?


I took photos, and I used the recommendation from Jimmy Stewart (in
Adam's thread), for imgbb ("simple and free"). It seems to do what it
says on the tin, and it's a _very_ good interface (what is their pound
of flesh I wonder?)

I made an album of 6 photos (all of which expire in two weeks time). It
is "Private but readable by anyone with the link" -- which is this:

https://ibb.co/album/6rnZ46

You can change the view to A-Z, which is the best as they are numbered:

1. What I saw yesterday, and sent me running straight to D-I-Y!
2. Close-up of the "gunge-mat".
3. I lifted a piece of the mat out and put it on the side.
4. Close-up of that piece.
(You don't need a pic of a clean expansion tank!)
5. and 6. are pics of the cold water tank, specifically the very cruddy
ballcock-works.


Hope this has been of interest to a few (what with learning about imgbb
as well as typing this, I think it's taken longer than this morning's
operation! :-D

Thanks _very_ much to those who offered opinions and advice!

John (Another)