On Mon, 15 Dec 2003 02:35:53 -0000, "Peter Taylor"
I agree and it's why I had suggested replacing the 15mm pipes in the
loft area at least as far as possible, to be replaced later if
I wouldn't go as far as to say that it is unsafe to have part of the
vent in 15mm, after all it would appear to have been like that for 30
years or more. Certainly it is normal and good practice to run in
22 or even 28mm tube.
Looking at the first photo again there is a vent pipe appearing at the
centre over the small cylindrical tank. It's not clear to me
whether that is part of the DHW setup or perhaps an additional pipe
related to the primary side to vent that. If so, then the
implication would be that there is an additional 15mm feed/expansion
pipe going to a point close to where that joins the primary circuit.
I already covered that one. Santa asked how to fit a cylinder stat.
There may already be a motorised valve, and if so, of course if that
is the case the feed and vent pipes should be connected on the boiler
side of it (on the flow from the boiler) and not at the cylinder.
I assume that the tank within the tank is the header unit for the central
heating, and the drum at the bottom is the coil for heating the cold water.
The expansion pipe certainly does come from downstairs, the boiler is in the
kitchen. The CH Pipes are 15mm and I doubt I'll be able to cut off and
change to 22mm any more than a couple of metres.
On Mon, 15 Dec 2003 22:57:32 -0000, "SantaUK" <Aye Right!!!> wrote:
THis really is a strange machine, isn't it.
It certainly appears that the horizontal cylinder at the bottom is the
heat exchanger. From the other shots, the implication is that the
short pipe coming up and over the vertical cylinder, bt not dipping
into it would then be a vent for that and potentially the whole
This leaves the vent pipe that comes up to the roof apex and loops
over as unexplained for the moment. However, since it is aimed over
the same small tank, it probably is another vent related to the
primary circuit possibly connecting near the boiler. I think that
it is pretty important to check where that pipe goes. If it is
another primary circuit vent, then it appears that it is in 3/4" or
22mm and would probably then be suitable as a vent for the new setup.
There are some unanswered questions, though.
1) There is no vent for the hot water tank. However it appears that
there is a lid. Was the whole tank wrapped in a lot of insulation
including the lid? Presumably it all became quite warm anyway.
Since the lid is a loose fit and there is a hole, perhaps the
manufacturers would not have an extra vent anyway. You would need to
ask them that question. It's not hugely important though, because
the Fortic tank deals with that itself anyway
2) Assuming that the small vertical cylinder is a header for the
primary circuit, I would expect to find two more things.
a) Some means for it to be topped up. Is there some arrangement that
does this from the small rectangular tank fitted to the side of the
main one? Presumably there is also something to provide water into
the main tank from the small rectangular one?
b) I would expect to find a small pipe from the bottom of the small
vertical cylindrical tank either exiting the main tank completely and
going to the boiler primary circuit elsewhere, or perhaps going to the
horizontal heat exchanger cylinder. Either is possible and the
latter would make complete sense.
Given that the above is true, and I would suggest checking with the
manufacturer, then you may well have an operational 22mm vent pipe on
the boiler primary. This is good news in that it can be used for the
new header tank if so. It would also mean that you don't need to
upgrade the pipes to the cylinder coil from the safety aspect yet,
you'll just get rather slow cylinder recovery.
The bad news is that this vent pipe may well connect to the boiler
primary circuit some way from the loft. If so, then connecting the
feed pipe from the bottom of the header tank to the cylinder coil
pipe as suggested yesterday would quite likely lead to pumping over of
water through this vent pipe or sucking down of air into the boiler
primary circuit. You don't want this happening because it will lead
to wasted heat and system corrosion. This would happen because a
pressure differential will have been set up between the two pipe
connecting points and is why they should normally be connected no
further than 150mm apart on a circuit pipe.
You could suck it and see, but the problem is that the cure is then to
arrange the pipework as it should be. Given that, it is probably
better to do the correct hookup in the first place.
This is why it's important to trace where the pipes go and also the
relative positions of the pump and motorised valve(s).
Regarding the header tank, given what you have, a good mounting
solution could be to build a small wooden platform near the apex,
above the level of the Fortic tank but allowing enough room to work on
the float valve if needed. You could fit a couple of horizontal
timbers to the roof trusses and then fit a piece of ply to it to take
On Tue, 16 Dec 2003 22:34:19 -0000, "SantaUK" <Aye Right!!!> wrote:
I suspect that it finds it way to the boiler somehow or at the very
least to a point on 3/4" or 22mm primary pipework that does not have
any pump or motorised valve between it and the boiler.
This is important for safety reasons. If the boiler were to fail in
a way that caused it to boil, there must be a clear path for the steam
at all times.
OK. Makes sense.
OK. So it looks as though what we have is that the small vertical
cylinder is indeed the header for the CH primary at the moment, as you
surmised. It has a feed and then the small vent is to let the air
out. The important vent from the safety perspective is not that one
but the one coming to the apex. It is probably there because there
is a motorised valve and possibly the pump between the heat exchanger
and the rest of the circuit.
No definitely not. Now that we know what this is, and that the
pipes to the heat exchanger are only 15mm or 1/2", it would not be at
all sensible to not use the vent that goes up to the apex.
However, to reiterate, I do recommend that you trace where this goes.
It probably does go to a correct point on the system, but given its
age and the fact that a new boiler was fitted I would double check.
Ideally, you should have a 15mm pipe from near the bottom of the new
feed/expansion tank following this pipe and joining about 150mm from
where it eventually tees into the rest of the circuit.
You *may* be able to get away with connecting this feed pipe to one
of the pipes connected to the heat exchanger as originally planned,
but if there is a significant pressure differential to where the vent
connects, then you will get pumping over from the vent or sucking down
of air. You don't want either. Personally, I would run in a new
15mm pipe and be done with it, because I suspect that there is quite a
high chance of one of these effects. You could even put most of it
in place before draining and disconnecting the existing tank.
I think that given the age and circumstances of the system, it would
be a very good idea to do a complete sketch of the circuit, starting
at the boiler flow and marking the relative positions of where the
pump is and the motorised valve(s) and the tee for the vent.
A sketch like you did before, and posted on your web site would be a
With the arrangement of not having either the vent or the feed
connecting to the coil in the Fortic tank, you will have created a
high point on the system. This is OK, but you will need an air
bleed fitting. Basically these are a 15mm fitting with a small
knurled cap that you turn to let the air out. Put a tee on the
upper of the two pipes to the coil with a 15mm branch pointing
upwards. Fit a short length of 15mm tube to that (say 20-30cm) and
put the vent fitting on the top. THen you can gently bleed the air
out after the system is otherwise full.
That's the easy bit.
To email, substitute .nospam with .gl
"SantaUK" <Aye Right!!!> wrote in message
| Fecking hell - nearly finished!!!
| Question - safe to use PTFE tape round the immersion heater ? Its leaking
| slightly. Might be better with a second seal.
I always think it's best to wrap a few turns of PTFE around the thread to take
up any loose bits.
On Tue, 16 Dec 2003 16:46:39 -0000, Christian McArdle wrote:
I was thinking more about the fact that the approval is required (plus
associated fees/paperwork) rather than any difficulty in complying with the
Why the government didn't just outlaw the selling of non compliant
cylinders, I don't know.
On Tue, 16 Dec 2003 17:48:55 -0000, Christian McArdle wrote:
Must admit I thinking of paragraph 2.3 c) in isolation, which only refers
back to the insulation requirements for the cylinder, forgetting the
paragraph d) that seems to have given rise to one of the longest recent
threads on here :-)
On Tue, 16 Dec 2003 17:48:55 -0000, "Christian McArdle"
It is possible to meet the insulation requirements of the referenced
British Standard other than by the use of a foamed cylinder by adding
appropriate other insulation. However, older cylinders may not meet
the reheat time requirements as a result of inadequately sized heat
exchangers. Even this standard is not that great in terms of the
heat exchanger, since modern boilers are able to deliver heat at a
greater level than a minimal BS cylinder can take.
To email, substitute .nospam with .gl
I know what you mean - physically - it isn't a difficult job - but
technically - cover all questions and answers before hand and all should go
well. Its just one of those jobs that if you find you haven't secured the
drain cock properly and have a tank full of water yer in the shit!
Done It!!! Well have to say - big thanks to Andy Hall for all his guidance,
not forgetting the others with input - much appreciated. A couple of
weeping compression joints, but I'll see to them tonight. That was fun!!!
I even set my alarm this morning for 03.30 to check for any issues YAWN!!!!!
It's a matter of experience in my book.
To begin with, you need to be sure that the pipe ends are clean, dry
and properly formed (olives won't take very well if the pipe is not
The only other thing I've come to realise is that you need to tighten
up the compression joints. I've recently taken to using a couple of
12in adjustable spanners ('King Dick' variety) for this job and now
have a fairly good idea of when a compression joint is tight enough.
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