Pressure rising in c/h system

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Hi everyone (thanks for your help so far BTW)
OK, at the weekend, I ran the hot tap in isolation and after a short pause, the header tank started to refill itself. So it is obviously filling the water cylinder which therefore cannot be mains pressurised. The pressure vessel is definately connected to boiler primary circuit.
The pressure gauge is located on the safety relief valve which passes through the outside wall next to the boiler (Danesmore Worcester 20/25 room sealed). I have seen the system rise to about 2.2 bar before I got worried and took some water off.
I haven't spotted any other filling loops.It's a bit difficult to tell what's happing in the airing cupboard, there are so many pipes and lots of stopcocks too. It could be one of those (but none of them are flexi hoses).
I would like to disconnect the filling loop, trouble is that it's not completely watertight when hot. I unscrew the flexihose from the non-return valve (which is on the c/h side), there are no leaks when cold. However, when the pipes are hot, you can see a little bit of water sitting in the top apeture of the non return valve fizzing and dripping constantly.
Can anyone recommend a female fitting to cap this off? I asked at my local plumb center and they had no idea what I was talking about! I measured the thread with verniers and it's about 19mm diameter. I could do with a male one for the open end of the flexi hose too.
Nick
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It's probably 1/2" BSP - so would need a 1/2" BSP female endstop.
As a way of verifying whether it is 1/2" BSP, see whether a standard shower hose screws onto it. If it does, it *is* 1/2" BSP.
Roger
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On Mon, 01 Dec 2003 10:48:46 +0000, Roger Mills wrote:

Or the end of any 15mm compression fitting.
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I had a look, I can't find one with a closed end. I looked at Jewsons, BES online and Screwfix online. Any ideas?
I could bodge on up with an ordinary compression nut, a coin and some araldite or something...
Nick
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On 2 Dec 2003 05:21:36 -0800, snipped-for-privacy@bt.com (NickW) wrote:

Nick, by the time you've mucked around, it would be a lot easier to just change the valve......
.andy
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On 28 Nov 2003 00:03:10 -0800, snipped-for-privacy@bt.com (NickW) wrote:

OK.
We should try to find out whether the pressure vessel is part of the boiler primary circuit or the hot water system. Likewise I would like to know where the header tank, which sounds to be the size of a CH header tank, fits into all of this.
If you could find a way to take photos and get them onto a web site or even ftp server somewhere it would be a real help.

Make and model would definitely be a help.
Generally what you describe would suggest an indirect tank with cold feed in at the bottom, one coil connection at the bottom, the other half way up and then the outlet from the top.
However, the various pieces that you have don't completely add up for me at the moment.
The pressure vessel could quite reasonably be part of the boiler primary or the hot water side. Can you identify which?
The role of the header tank is also unclear. If the system is sealed on both sides, I can't see a reason for it being there. Again, knowing where it connects to would be useful.
It sounds as though you might either have some kind of a heatbank/thermal store system or perhaps a much older system that has been converted to sealed operation and some of the pieces left in place.

.andy
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I am 99% sure it's connected via a tortuous route to the pipe that goes into the h/w cylinder halfway up ie: the boiler primary circuit.

I hear the tank refilling when I run a bath but this could also be because the cold water tap is on at the same time! I'll check tonight.
I've a feeling we are going to find it's not related to the h/w cylinder because I was using h/w in the summer and the problem did not occur!
The only thing I can think of is that
a) The filling loop opens of it's own accord, maybe when the radiator pipe it's connected to gets hot. I disconnected it when cold and both the tap and non return valve both function (I disconnected it without turning the mains off or draining the c/h system).
b) There is another filling loop I haven't spotted...
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On 28 Nov 2003 06:30:34 -0800, snipped-for-privacy@bt.com (NickW) wrote:

Right. Then it's likely to be for the boiler primary circuit.
However, according to the manufacturer's literature there are some Danesmoor models which are system boilers and they mention that for sealed systems these contain an expansion vessel. Often this is large enough for the complete system , but in a system with a large number of radiators an additional vessel may be required. If there is no obvious vessel inside the boiler when you take off the front panel then the one you have is it for the boiler primary.

If we could determine the exact function of this little tank it would help, then we can eliminate it. It would be a bit bizarre but not impossible if it were a small header tank for cold water for the bathroom, however it's a bit small.
Can you find out if it fills only when cold water is used, or when hot is. If it is either, then you don't have a pressurised hot water system and the cylinder is not where the problem is likely to be. Can you also check the pressure at the taps by holding your hand over the spout and turning on the tap. This will also tell you if the HW system is mains pressure. So far, there is nothing to confirm that it is.

I have also been thinking this, except for the possibility that there might be a small pinhole in the cylinder coil or somewhere which opens up with temperature. However, this does not completely explain the summer/winter effect. Is there just a simple motorised diverter valve to direct boiler water flow to cylinder or radiators or is there anything more complex that you switch over from summer to winter?

Try disconnecting it and leaving it disconnected. You should really, anyway,.

If we can eliminate the cylinder then yes. Either that or there is somewhere where perhaps the plumbing was modified at some time in the past or when the system was changed to sealed that is in some other way connected to a source of higher pressure.
As a matter of interest, where is the pressure gauge that you are reading and what are the values when you take water out and afterwards?
.andy
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snipped-for-privacy@bt.com (NickW) wrote in message

Unless I've missed it somewhere in this thread, you haven't yet checked whether disconnecting the filling loop cures the problem? Needs ruling out, especially given that (as somebody else has pointed out) it should not be left connected anyway, by rights.
David
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On Thu, 27 Nov 2003 09:38:55 +0000, news.mistral.net wrote:

Is it possible that this a thermal store with boiler primary and DHW indirect coils?
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On Thu, 27 Nov 2003 20:01:56 +0000, "Ed Sirett"

Wouldn't it have to be under mains pressure in the bulk of the water in the store in order that water is forced from the store to the boiler primary circuit?
.andy
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On Thu, 27 Nov 2003 20:18:10 +0000, Andy Hall wrote:

Yes it would, I realised that after I had posted. I think it is time for the OP to give all the details of the syetem and preferably some pics.
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Just a thought but,
Have you tried bleeding your radiators? It could be that you are getting a hydrogen build up somewhere.
That would certainly explain the symptoms i.e no build up in the summer (most chemical reactions are much slower as temp goes down, approx half for every 10 degrees C) The hydrogen will take up far more space at even 3bar than the equivalent number of moles of water. (I think the reaction goes something like 2 moles of H20 plus one mole of Iron gives 2 moles H2 (taking up about 22 litres at STP) plus 1 mole rust (FeO2)) Possibly, adding some inhibitor might help. If the above is the case, ironically you will probably also need to top up the system (once it has been bled)
I partly put this forward because it is exactly what happened in my system!
Stephen

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On Wed, 26 Nov 2003 13:16:03 -0000, "news.mistral.net" <sadf> wrote:

That thought crossed my mind as well, but quite a substantial amount of water is having to be taken from the system regularly, and if H2 build up were the main culprit, the radiators would empty and be cool at the top
Certainly inhibitor should be used, but my guess is that we are looking at some form of leak here - the amount of water and regularity is too much
.andy
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snipped-for-privacy@bt.com (NickW) wrote in message

Sounds like you have air in the ch system, which expands as it heats up causing the pressure rise. Try leaving the filling loop unattached while you use the c/h; my guess is that the pressure will still increase. Have you tried bleeding all your radiators / boiler?
David
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On Tue, 25 Nov 2003 23:56:51 +0000, NickW wrote:

See FAQ. Possibly its corrosion of some sort?
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snipped-for-privacy@bt.com (NickW) wrote in message

Hi, This is what you must do as the first part of the fault elimination process. 1. With the system cold, remove the filling loop 2, Drain down the system, not completly but untill the pressure gauge reads zero. 3, using a standard tyre pressure gauge, measure the pressure in the Expansion Vessel, it should be 15-20 psi. The expansion vessel is shaped like a big red victorian Bed Warmer my bet is the gauge will read zero, if this is the case use a car foot pump to increase the pressure. If the EV is faulty leave it where it is and fit a new one using a conex tee at a point somwhere on the ground floor if the EV has 15-20 psi in it let me know and we will go onto step 2 (the English book of Common Prayer) regards Bob
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