Strange gunge in header tank

[niggle45]

Just had the man out to fix the boiler under warranty (only 8 mnths old) and he discovered a brown/black skin covering most of the surface of the header tank in the loft. A bit like the skin on custard in consistency (not colour), maybe about 1-2mm thick and clinging to the sides of the plastic tank. He has never seen it before & when I described it to the installer, neither had he.

The tank is covered (not quite completely) by plastic covered lagging and the water in the main tank (supplied by the same feed) is perfect.

This has obviously appeared only over the past 8 months.

Has anyone else come across anything like this? Any ideas about prevention would be gratefully received.

 

[Blake]

What colour is the water in your system and was it fully flushed prior to the new boiler going in ?

 

[stani]

I've also recently cleaned out a system with exactly the same stuff only about 30mm thick, had a seriously bad smell, at first I thought it may have been an animal which died but there were no bones,the only other suggestion I have is that a mix of cleaner and other stuff (inhibitor possibly) had made this react, this header tank was in a property which was rural apart from that i have no other ideas either

 

[diamondgas]

Sounds like some bacterial growth. If the water in the expansion tank is kept warm it's a lovely place for bacteria to grow. It's a pity the installer didn't want to make your system a sealed system.

Best way to clear it is remove the tank and disinfect. You may have other design issues that could be putting excess heated water into your header by the way.🙁

 

[niggle45]

That was quick -didn't expect replies so fast. Thank you all for your comments.

The colour of the water now is brown but I am not sure if system was flushed properly at installation. I (perhaps naively) assumed it was. Probably unable to speak to installer now until after Bank Hol to check!

Funny you should say that - Diamondgas. The reason for the call out was that the heat exchanger was "kettling" and I guess it is possible that hot water was being fed back into the header tank.

There is a definite smell from the tank now, but I think this is the cleaner I put in (on instructions from the repair man).

 

[diamondgas]

I hope it wasn't acidic!! Whatever you put in there ends up circulating around your radiators and lovely new boiler! What did he ask you to put in?

 

[Plumbstar Tom]

Whats it taste like? Only joking please don't eat/drink it

Get your plumber to pop a cleaner in it then drain and add an inhibitor

 

[Mikey456]

Hot water will be fed into the header tank anyways. When the water heats up it needs somewhere to expand so your always gonna have some hot water being fed back there

 

[niggle45]

Mueller Primaflow Central Heating Cleaner which is described on the COSHH
sheet as a "Proprietary blend of poly-acrylic acid and organic dispersing agents" with a pH of 3.0 - 4.0 (concentrated)!

I understand that it needs to be flushed out in 2-3 weeks. Hope this is OK!

 

[diamondgas]

Hot water will be fed into the header tank anyways. When the water heats up it needs somewhere to expand so your always gonna have some hot water being fed back there

Hi mikey456,
Whether hot water arrives in the header depends on a few factors and doesn't necessarily mean the header will ever get 'hot' hopefully it won't! It all depends on the size of the heating system as well as installation issues. The expansion pipe will accommodate the expansion of water in the heating system as it heats up. If there's enough water in the expansion pipe then the hot water expanding up it may never reach the tank. I'm sure there's a way of calculating how much a system will expand but who remembers that bumf? It is important to accomodate expansion water within that pipe though i believe and not the header! Someone will know?

 

[diamondgas]

Mueller Primaflow Central Heating Cleaner which is described on the COSHH
sheet as a "Proprietary blend of poly-acrylic acid and organic dispersing agents" with a pH of 3.0 - 4.0 (concentrated)!

I understand that it needs to be flushed out in 2-3 weeks. Hope this is OK!

Well that sounds like system cleanser to me 🙂 I thought for a minute they'd suggested Domestos!!!

 

[WHPES]

In my experience it usually goes like that when a mouse or rat falls in and rots. Check the debris for fur and bones, then clean out and buy a lid!

If you find this is the cause then do check the lid on your DHW cistern is closely fitting with no gaps and to WRAS regulations as if mice fall into it you have a health issue. Bear in mind mice can squeeze through less than 1cm gap.

 

[stani]

In my experience it usually goes like that when a mouse or rat falls in and rots. Check the debris for fur and bones, then clean out and buy a lid!

If you find this is the cause then do check the lid on your DHW cistern is closely fitting with no gaps and to WRAS regulations as if mice fall into it you have a health issue. Bear in mind mice can squeeze through less than 1cm gap.

I definitely checked the system I cleaned out for bones etc and there was absolutely nothing in there, that was my first assumption
especially eith it being a rural property.

 

[plumberdarren]

ph of 3 is quite acidic surely thats not very good for the heat exchanger especially if its left in for a few weeks ?

 

[niggle45]

Drained and removed tank but no identifiable residues (e.g. bones) could be seen, just brown sludge. Tank now cleaned, disinfected and thoroughly rinsed. Flushed entire system through until clear (not that it was that bad) and refilled. Lid is the next job!

All seems to be working OK so will keep a watchful eye on the state of the tank in future.

Many thanks for all the interest and suggestions.

 

[diamondgas]

Drained and removed tank but no identifiable residues (e.g. bones) could be seen, just brown sludge. Tank now cleaned, disinfected and thoroughly rinsed. Flushed entire system through until clear (not that it was that bad) and refilled. Lid is the next job!

All seems to be working OK so will keep a watchful eye on the state of the tank in future.

Many thanks for all the interest and suggestions.

Fingers crossed it resolves your issue 'niggle45'! 🙂

 

[darrenangel]

It could be the inhibitor was put in the header tank after the system was re-filled. This would not then enter the system and this can turn to a jelly like substance.

 

[Dave-w]

Hi I have experienced exactly the same issue after having a new system boiler fitted 2yrs ago. System was power flushed first and had never previously had an issue. Fernox F1 inhibitor. After 12 months a skin 20mm thick had formed. Tank emptied and cleaned with bleach, dried and refilled. After another 6 months a similar skin had reformed but only about 5mm thick. Cleaning and refilling repeated. Now, after a further six months, skin is beginning to reform by agglomeration of smaller floating brown 'islands'. Worcester-Bosch and local plumbers flummoxed.
Anybody got any ideas what is going on?
Dave-w

 

[Dotty]

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