Brown-orange Sludge in Feed/Expansion Tank

Marcoo

Marcoo

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Hello everybody,

I am experiencing an annoying and on-going problem with my central heating, and I was wondering if somebody could help me understanding a bit more of what's going on!
A bit of background:
-Type of system: Vented system, with F/E tank in the loft, combined feed and vent.
-November 2014: New boiler installed, and performed the power flush of the whole central heating as suggested (British gas did it).
-July2015: I went up in the loft and found a thick orange foam in the expansion tank. I call British gas again and they cleaned the F/E tank and put a whole bottle of Fernox cleaner (I think, but the bottle is still in the loft if more info are needed).
-November 2015. I go up again in the loft and I see again that orange/brown foam! please see picture below.

Now... what's going on? The system was cleaned only 4 months ago, and power flushed 12 months ago!
I don't think this is normal... What could the cause be? I really want to keep my system in a good state as I invested quite a lot of money in a decent boiler only 12 months ago...

Please let me know if you need more info, I can try to find out!!!

Many thanks in advance for your help!!

cheers!

Marco

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Rusty gunge coming from the boiler and radiators....the iron or steel parts of the system.
It's unlikely that a power flush would clean what you have here.....best to get in there with a wet vac and suck it out.
The water doesn't change much in this area, hence the 'stagnation' if you like. If your radiators refuse to bleed at any time, the cold water feed to them from this tank will be blocked - usually where it joins the heating pipes.
John :)
 
Thanks John for the super quick reply!
I hoped the power flush + lots of cleaner/inhibitor would had done the job... Even if I clean up the F/E tank, I suppose it is highly likely I'll get it back fairly soon... what could be the underlying cause that leads to such a fast rusty gunge build up? any other "symptom" I may have to look for?

Cheers!

Marco
 
I have found that the odd grungy bubble tends to leave the central heating pipes, and travels up the cold feed, where it resides in the loft tank.
The inhibitor in the system tends to produce some foam when exposed to the open air.
From time to time, I'd be inclined to bale out this tank, but of course you don't want to introduce fresh water into the system due to the high oxygen content.....therefore, tip some inhibitor in the tank as it fills.
The rust will return, obviously, but hopefully the inhibitor within the system will minimise this. Obviously the older the system and radiators, the more rust there will be.
The same gunge actually resides in the radiators themselves, but it's black there due to the lack of oxygen.
John :)
 
Many thanks John, very clear explanation.
I will clean up the FE tank as you suggest and add some more inhibitor (I think I have a bottle of Fernox F1 in the system at the moment, I'll add a bit more of it).
Any other liquid I should add in the FE tank after the cleaning? I live in a hard water area, so limescale build up is also likely to occur..

Cheers!

Marco
 
You need to be in the loft looking at the tank when the system stops. Could be that the systems pumping over due to either the pump speed being too high or /and the vent pipe not being high enough resulting in pump over into the tank
 
Definitely the next thing to look at......the expansion pipe isn't visible from your pics but it should curve above the tank so that anything that comes out of it splashes back into the system.
The level of water in the expansion pipe is the same as the water level in that tank when the system is off......can you see if the expansion pipe has any drips on the end of it?
John :)
 
If you can suspend a plastic cup or similar under the vent pipe, pop back a day later and see if there's any water in it.

If there is, your system is pumping over and massive corrosion will be taking place.

If it is dry, remove it, shut the loft hatch and stop worrying.
 
Just re-read......combined feed and vent here but the level looks fine - I guess a bale out from time to time wouldn't go amiss though.
John :)
 
If the cold feed from the expansion tank gets blocked with crud (as mine has) does that also mean there might be a blockage in the vent pipe? I never checked but wonder if I should
 
Thanks guys for all the replies, just managed to read them now.
Yes, I have combined feed and vent (you can partially see the reflection of the pipe at the bottom of the picture). So I'll clean it up over the weekend and keep an eye on it... It just looks strange to me that so much foam/sludge/*** built up since July when the tank was cleaned by British Gas...
Again, thanks a lot for your suggestions!!

cheers,

Marco
 
After a bit of delay on the original schedule, I finally managed to clean the FE tank over the weekend. The whole gelly orange/brown "stuff" turned out to be a pretty thick film on the surface, which was easily removed in one piece using sieve! It looks like whatever was in the system reacted with air creating this film. I added a bottle of Fernox F1 while refilling the tank.

After that I realised that the British gas guy left a whole bottle of Fernox F5 (Central Heating Powerflushing Chemical) circulating in the system since last July. Could this be the cause of such orange sludge? As I only emptied the FE tank, it is still in the system... Is this going to create any problem or it can stay in? I have a magnetic filter that should pick up any loose debris circulating in the system.

cheers!!

Marco
 
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