CH feed/overflow tank - gunge

[Another John]

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.

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.

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?

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!

John

[Steve Walker]

I don't know if it was related, but my system had no inhibitor for years (I'd refilled after some changes and never got around to it). When I added some, a horrible scum soon formed in the tank!

[Martin Brown]

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

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.

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.

Was there any inhibitor in the system?

[Brian Gaff (Sofa]

I guess any gunge in the system has to end up somewhere! Can it not simply be scooped out and the water in the tank filtered somehow so it can start from scratch, Maybe done when the heating is off.

Obviously! Brian

[alan_m]

I've seen the same with a floating light brown layer in an insulated plastic tank with lid and with inhibitor always used in the system. I found the gunge to be the consistency similar to that of a weak wall-paper paste and around 5mm deep. I turned off the service valve to the tank and used a wet and dry vacuum cleaner to empty the tank - a PITA as the tank held more water than the vacuum cleaner could suck up in one go, and it needs to be emptied. The tank may have experienced some short periods of pumping over during its life in the loft so at some time it may have contained hot water.

I agree that its not something I would want going into a micro-bore system and I'm not sure that anyone servicing the boiler would consider emptying the loft tank in a way that the crude doesn't enter the system to be part of the boiler service.

[Another John]

OP here -- thanks very much for all replies so far: useful I especially like Alan's suggestion of using a wet/dry cleaner for emptying the tank.

Ooh - that's a bit technical for me Martin! You won't find a less-science-educated duffer than myself!

But I will attempt a picture tomorrow ... before I get the vac. out!

John

BTW - what do I use for publishing pics these days? I always used to use Tinypic, but it's looked rather grotty to me the last couple of times I used it. [Update: In fact I've just seen that Tinypic is deceased.]

[wasbit]

Postimage -

[Radio Man]

I?ve seen one with some nasty stuff which looks like brown pond weed I think is from being repeatedly topped up with inhibitor. I suggest you clean the tank drain the system fill with water and cleaner run for a week or two then flush. Then refill will fresh water and inhibitor.

The system should be flushed every few years ideally with a hose.

[Another John]

You could be right Radio Man -- I am guessing that the system has never been flushed since 2008, when the new boiler was installed (along with more pipework, rads, and this expansion tank), but that inhibitor has been added a couple of times by visiting plumbers, or even by myself (don't ask me what hey, or I, might have been doing: 'the past is a foreign country' to me now).

To add emphasis to it, I'm about to add another part to this thread, because I think I have fixed the problem. !!!

John

[Another John]

OP here: 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 shit 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:

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)

[Andrew]

Are you in a hard water area ?. I get cruddy deposits on my cold tank ballcock like yours. I'm not sure if there is a solution, maybe remove, clean off deposits with vinegar or other mildly acidic substance and then smear with grease before replacing.

Brass ballcocks are not that expensive though. I keep a couple in 'stock' as spares.

Tanks should be covered and insulated in such a way that no light can penetrate the tank because this encourages algae, and there are micro orghanisms that can grown in a hostile environment like your C/H header tank.

[Scribbles]

Last month, on the coldest weekend of the year, my CH entirely ceased to function. Like the OP describes, it's a piecemeal system, some parts being close to 50 years old. When we moved here in 2017, we had the system cleaned out and a new boiler installed. Everything was fine until early February when a series of faults coincided. A very expensive month and some complex work by the CH engineer has resulted in a brilliantly improved system but my problems were partly due to a corroded loft tank containing the sort of gunge described above. This has now been replaced by a new tank, made of non-corrosive material and supplied with a cover as recommended by my CH guru. The idea is to prevent detritus from outside getting into the tank - dust and grit, pigeon droppings, dead rats, etc. So I think the answer is yes, covering your tank can only be a help.

[Radio Man]

You're welcome. I hope it stays clear.

[Martin Brown]

Leave it alone until it fails. Water splashes dry and deposit tiny amounts of calcium carbonate. It looks bad but does no real harm.

Even on the cold tank it is surprising how a few splashes can contrive to jump out when the lid is not on the top. And more importantly it prevents ingress of dead flies, bats, pigeons and any other wildlife.

Something waterproof is much better. Otherwise you will have a soggy mouldering wet thing up there causing trouble. I ran my hot header tank without its cover on for a couple of hours whilst testing the immersion heater. It would have totally messed up the loft humidity like that.

[Another John]

Thanks a lot Martin -- very helpful.

John