system capacity in litres ?

Gasguru · 15 Aug 2006

As Chris says pre-charge is probably low.

Release water and drop the system pressure to zero. Check vessel pressure is around 0.7 -0.8 Bar (assuming normal 2 storey house).

I normally find small flats about 2 1/2 buckets, larger flats 2 1/2 - 3 1/2 buckets etc.

On larger houses I normally stick a 35 litre vessel on top of the cylinder or up in the roof and double dose the inhibitor. The pressure doesn't rise more than a quarter of a bar from cold to hot. No large pressure swings to stress the system and the vessel will last years before a re-charge is required.

chrishutt · 15 Aug 2006

Gasguru said:
On larger houses I normally stick a 35 litre vessel on top of the cylinder or up in the roof .

Larger than what...Buckingham Palace? 35 litres is a bit OTT for anything remotely normal.

doitall · 15 Aug 2006

it easy enough to work out anyway without the guess work

Volume of rads is in the manufacturers info.

Boiler volume is in the instalation book.

Pipework, just measure the total lengths.

8mm 0.036 l/m
10mm 0.058 l/m
15mm 0.145 l/m
22mm 0.321 l/m
28mm 0.539 l/m

Gasguru · 16 Aug 2006

35 litre vessel only £35.00. Cheap compared with pump replacement if the pressure sits at zero for any lenght of time. And it comes with 3 little legs for it to sit on.

The pre-charge in the smaller vessels is pratically gone after a ccouple of years. The qaulity of Zilmets etc is nothing compared with the old W+P vessels.

corgiman · 16 Aug 2006

but that said can you install an external expansion vessel on this boiler I several that you cannot???

err that said the only one that springs to mind its the poxi 105 instant

doh

chrishutt · 16 Aug 2006

corgiman said:
can you install an external expansion vessel on this boiler

Surely any boiler can have an external expansion vessel attached to the return pipework. Why should there be any problem with any boiler?

corgiman · 16 Aug 2006

well chris if its a combi with a diverter valve you you be taking the expansion vessel out of the loop when in hot water mode, or, like the poxi 105instant if they use some of the expansion vessel for preheat.

I know that some manufacturers do not like you fitting an external vessel, these are in the minority but still worth asking them.

chrishutt · 16 Aug 2006

But the expansion vessel would still be connected via the flow connection (unless say all TRVs were shut). In any case in DHW mode there wouldn't be much expansion to accommodate, so it's hard to see how there could be a problem.

Softus · 16 Aug 2006

I've never pretended to know everything about boilers, but this is confusing to me...

corgiman said:
well chris if its a combi with a diverter valve you you be taking the expansion vessel out of the loop when in hot water mode,

Why would the EV need to be in the loop for DHW?

...or, like the poxi 105instant if they use some of the expansion vessel for preheat.

I really don't get this: the same EV is used both for absorbing the ebb and flow of CH pressure, and for preheated DHW? Shurely some mishtake?

bripl · 16 Aug 2006

softus wrote
really don't get this: the same EV is used both for absorbing the ebb and flow of CH pressure, and for preheated DHW? Shurely some mishtake?
no mistake just poor design.

corgiman · 16 Aug 2006

Softus said:
I've never pretended to know everything about boilers, but this is confusing to me...

corgiman said:

well chris if its a combi with a diverter valve you you be taking the expansion vessel out of the loop when in hot water mode
Why would the EV need to be in the loop for DHW??

Click to expand...

Not for the DHW soft but for the expansion of the heating primaries, to and from a back to back dhw heat exchanger, but as chris says there would not be much expansion but enough. so i would like this previous comment of mine stricken from the record

cos i am a plum

:

Softus said:
or, like the poxi 105instant if they use some of the expansion vessel for preheat.

Softus said:
I really don't get this: the same EV is used both for absorbing the ebb and flow of CH pressure, and for preheated DHW? Shurely some mishtake?

Nope Poxi seperated the expansion vessel to create a preheat store, effectivley halfing an already inadequate expansion vessel, hence why they split all the time, the DHW and CH are seperated.

Not saying that you MUST NOT fit an external expansion vessel to a combi, just saying that a ten minute phone call to the manufacturers would be advisable before you do

Softus · 16 Aug 2006

corgiman said:
Not saying that you MUST NOT fit an external expansion vessel to a combi, just saying that a ten minute phone call to the manufacturers would be advisable before you do

Yup - I understand your point here, however...

Softus said:
Softus said:

or, like the poxi 105instant if they use some of the expansion vessel for preheat.

Click to expand...

I really don't get this: the same EV is used both for absorbing the ebb and flow of CH pressure, and for preheated DHW? Shurely some mishtake?

Click to expand...

Nope Poxi seperated the expansion vessel to create a preheat store, effectivley halfing an already inadequate expansion vessel, hence why they split all the time, the DHW and CH are seperated.

I still don't get it. If the EV is seperated then there are two EVs, and adding an external one on the CH circuit would have no effect at all on the DHW EV.

corgiman · 16 Aug 2006

from parts arena

I dont know how to post a pic

1.2 Instant Domestic Hot Water (Expansion Vessel & Pre-Heat Store)
1. The boiler expansion vessel incorporates a small volume of stored primary hot water.

2. When the boiler has been off and there is then a demand for domestic hot water the stored primary hot water ensures that domestic hot water is supplied instantly at temperature.

3. The stored hot water is part of the primary circuit. This is not supplied as domestic hot water, which is fresh mains water heated by a heat exchanger within the boiler.

4. The stored primary hot water temperature is maintained whilst the boiler is in operation. During a period when there is no demand for heating or hot water the temperature of the stored primary hot water will eventually fall. The boiler will operate occasionally in order to maintain the temperature. This is indicated by the domestic hot water mode neon flashing.

Sorry I am wrong its keeping the ch water hot for the heat exchanger, It is late

Softus · 16 Aug 2006

corgiman said:
It is late

Too true bruv'

Gasguru · 17 Aug 2006

Poxi expansion vessel http://v3.espacenet.com/textdoc?DB=EPODOC&IDX=TR9902491&F=0

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system capacity in litres ?

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