Thursdays Job - Change Hot Water Tank

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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 appropriate.
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.

.andy
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That pipe comes from below the loft - I will investigate tonight to see if I can get any info on it.
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SantaUK
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Just emptied the tank again and took more photos:
http://homepages.nildram.co.uk/~mmillar/CHWater.jpg
http://homepages.nildram.co.uk/~mmillar/topdown.JPG
http://homepages.nildram.co.uk/~mmillar/overview.JPG
http://homepages.nildram.co.uk/~mmillar/emptytank.JPG
http://homepages.nildram.co.uk/~mmillar/Expansionlid.JPG
http://homepages.nildram.co.uk/~mmillar/Closeupofch.JPG
http://homepages.nildram.co.uk/~mmillar/Expansionpipe.JPG
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.
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SantaUK
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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 primary system.
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 the tank.

.andy
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Agree with that!

And would probably be vented near the boiler though?

No other insulation than what you see in the pictures. The lid is loose (and damn hot when I pick it up)

Not easily visible, think I'll drain it down tomorrow night.

The latter is what exists.

Okay - so could this pipe be capped once identified and a new pipe fitted in the loft to the header tank?

Already planning that one ;-))
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SantaUK
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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 good idea.
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.
.andy
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Fecking hell - nearly finished!!!
Question - safe to use PTFE tape round the immersion heater ? Its leaking slightly. Might be better with a second seal.
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SantaUK
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"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. | | | Regards | | SantaUK |
I always think it's best to wrap a few turns of PTFE around the thread to take up any loose bits.
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On Sun, 14 Dec 2003 16:15:38 -0000, SantaUK wrote:

Did you know that replacing a hot water is now "building work" and therefore requires building regs approval? Daft but true.
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But only for Part L1 for energy efficiency. An unvented system is also Part G, IIRC.
Provided you update your controls and use a Part L approved cylinder, it won't be a problem.
Christian.
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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 regs. Why the government didn't just outlaw the selling of non compliant cylinders, I don't know.
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Because just using a Part L marked cylinder isn't enough. You also need to install zoning (if appropriate), a cylinder thermostat and boiler interlock, if these weren't already provided.
Christian.
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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 :-)
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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.
.andy
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"SantaUK" <Aye Right!!!> wrote in message

just
to
metric
well done on atempting this job! most people would not bother to learn sommat new and instead prefer to throw wads of dosh at a plumber!
good on ya!
steve
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<Chuffed>
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!
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SantaUK
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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!!!!!
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SantaUK
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On Fri, 19 Dec 2003 11:10:10 -0000, "SantaUK" <Aye Right!!!> wrote:

Well done.
How did you hook up the new feed/expansion tank in the end?
.andy
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"SantaUK" <Aye Right!!!> wrote in message

guidance,
Given the negative comments about plastic plumbing recently, does anybody get ALL compression joints watertight first time - and if so how ?
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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 perfectly circular).
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.
PoP
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