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!
[Posted from google since ntl's newsserver seems to be currently
If Ed's right about the flakes being a mixture of chalk (scale) and
oxides then acid should break it down. Chemicals are your best
chance: pressure flushing will probably be relatively ineffective
once there's a passageway through the heat exchanger the flow will
go through that leaving other parallel passageways blocked.
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...
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-
Hey, at least the sun is shining and the boiler still 'works'... ;-)
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.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
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.
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!
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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