Cleaning a heat exchanger?



For what it's worth I noticed that the Fernox DS3 is actually 'Sulphamic Acid' - I see various mentions of it on t'web saying it is suitable for rust removal as well as scale so I've got high hopes!
Mathew
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Mathew Newton wrote:

I keep a tub of 10% diluted to stick the shower head in. I think the advantage with sulphamic is that it's a strong acid but is easy to handle, with no fumes
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[Posted from google since ntl's newsserver seems to be currently pantsed]
wrote:

If Ed's right about the flakes being a mixture of chalk (scale) and iron oxides then acid should break it down. Chemicals are your best chance: pressure flushing will probably be relatively ineffective since once there's a passageway through the heat exchanger the flow will go through that leaving other parallel passageways blocked.
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Hmm... Took the heat exchanger to clean out today....
Unfortunately the last couple of days have been okay for HW - the CH flow pipe is still getting hot but the HW is a stable at a hot temperature. Bloody typical of course as it means it's hard to see if I've fixed things... but the hot CH flow pipe is a persistent issue so I guess that's the indicator.
I took the heat exchanger out and found it was actually pretty clean - the secondary side seemed spotless in fact, and the primary rather black. A few hose-throughs brought out quite a bit of black flakes... pictures below...
http://www.newtonnet.co.uk/house/boiler/heatexchanger /
There wasn't much though, and indeed the inline strainer pictured hardly had anything in it (and the CH water was a darkish yellow... not brown and certainly not black).
I pumped through some DS3 and this got rid a lot of the stuff and I'm sure the flow through it with the hose seemed to improve.
So.... I put it all back together again and, unbelievably given the WB CDi series is designed to spring a leak following any work on it, got a watertight assembly first time!
A HW demand however still produced a hot CH flow pipe.... but didn't cut out at all (although as mentioned is hasn't the last couple of days anyway). I'm sure the shower feels better (hotter at higher flow) but whilst this may be psychological the cleaning out must've helped.
So now I'm thinking it's the divert valve sticking. Given the price I may just fit a new one - I don't fancy taking mine out to inspect/ clean, particularly if it is beyond repair.
Any thoughts from your guys would most welcome again.... I wondered if some cleaner (X300?) in the system might help free the diverter up (if it is indeed sticking or not moving far enough)...? The primary heat exchanger sounds like it's heading towards kettling at some time in the not-too-distant future so maybe this would be a good double- whammy.
Hey, at least the sun is shining and the boiler still 'works'... ;-)
Mathew
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wrote:

Cleaning out the system is well worth it, while you are at it. Kettling sounds may be the giveaway clue. Try Fernox cleaner as it is more acidic. Flush and add X-100.
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On Sun, 11 May 2008 08:39:45 -0700, Mathew Newton wrote:

Does the CH pipe heat up after the HW has been run or whilst the HW is running? The former this is normal operation. It is also possible that the DHW flow diaphragm is not pushing the diverter valve 100% is it has a small split in it. I doubt X300/X400 will improve things.
The leakage into the CH might only be a few percent and possibly the cure is worse than the condition?
--
Ed Sirett - Property maintainer and registered gas fitter.
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It occurs during HW operation (as well as post-HW on occasion as is correct behaviour as you say).

The diaphragm is moving sufficiently far to fully activate the microswitch.. And I think I am right in saying that on this diverter the diaphragm doesn't actually move the diverter but rather effectively moves out of the way to allow the diverter innards to slide across/out (presumably under force from the flow in the primary). I say this because when I replaced the diaphragm a few years ago (d'oh - should've done the whole valve!) I noticed there the only contact between the diaphragm and diverter cylinder was the head of the diaphragm rod i.e. it could push the diverter cylinder, or stop it moving, but couldn't pull it (if you see what I mean).

Yeah I guess... certainly if the HW operation remains stable as it is at the moment then I could probably ignore it... either in the hope that it will go away or until a new valve pops up on eBay for next-to- nothing which seems to happen on occasion.
The other part of me is wondering how much life this boiler has got left in it... for a 'modern' boiler it's probably not doing too bad for 11 years and not having much wrong with it along the way.
Mathew
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On Sun, 11 May 2008 12:19:26 -0700, Mathew Newton wrote:

IIRC there is bloddy great spring inside the diverter valve which moves it back to the start.

For a quality make like WB 11 years should only be mid-life. However all combis of this generic design from all the makes seems to perform worse than C21 models.
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There is - but the start is CH mode!

I did wonder - maybe I'll keep it going for a wee while yet then. By the way, what's 'C21'?
Incidentally, I cannot help feel that the 24CDi was not designed to be easily repaired - it feels like open heart surgery to work on practically anything within it. Is this normal? I'm wondering if there are any boilers out there that are a little more DIY-friendly as whilst I get satisfaction from repairing this one I don't particularly appreciate removing perfectly good parts just to get at what I'm trying to fix... and I always hold my breath having reassembled it...
Perhaps I'd be better off with a non-combi next time as whilst I may have to find space for the external gubbins the slight avoidance of the 'eggs in one basket' aspect is appealing... oh how I dream of having a nice simple immersion heater as backup!
Mathew
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wrote:

Look at an Atmos. The pressure vessel hinges out of the way. A dream to work on. The best designed combi around. They just don't go wrong. http://www.atmos.uk.com/product_group.asp?section 0200130003
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Doctor Drivel wrote: <snip>

Obviously didn't see Doctor Who the other week. :-)
--
Rod

Hypothyroidism is a seriously debilitating condition with an insidious
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Yes, but it says it in the data sheet so it must be right.
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Matt, Dr Who is always right?
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In the outlet of the copmbi install a 9kW instant eclectic heater. This is small and can be under the sink. Have it off and the combi hot water just runs through it. If the combi is down then switch on. Simple. It will do a shower and even two taps at the same time. Or buy an Atmos combi - they don't go wrong.
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On Mon, 12 May 2008 14:26:32 -0700, Mathew Newton wrote:

Yep.
21st Century.

No idea.
--
Ed Sirett - Property maintainer and registered gas fitter.
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