Expansion Vessels

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Dazzyb

I have an Arston Microcombi 27 MFFI.
The boiler has since kept losing pressure (going from 1 bar to zero over 2 week periods) so I emptied some water from one of the radiators to act as an additional expansion vessel and now the boiler doesn't lose pressure.
The exp vessel in the boiler holds 6 litres and is set to 1 bar pressure. If I buy a new exp vessel to fit externally does anyone know what size I need and should it still be charged to 1 bar pressure?
If fit one externally should it go on the flow or return? The one currently in the boiler is in the return.
Cheers

so I emptied some water from one of the radiators to act as an additional expansion vessel and now the boiler doesn't lose pressure.

How does emptying water from a radiator act as an expansion vessel?

If you want to size your new expansion vessel correctly you need to calculate the water content of your radiators.

The vessel is best put on the return as it is colder and thus the membrane in the unit lasts longer.

How does emptying water from a radiator act as an expansion vessel?

You can compress a gas but not a liquid.

Expansion vessels are full of air. It is best to separate the air from the water with a membrane, but temporarily it works fine. Just like a Megaflo in fact.

Why would one have to add an expansion vessel to add new radiators? How would draining a radiator act as an expansion vessel?

so I emptied some water from one of the radiators to act as an additional expansion vessel and now the boiler doesn't lose pressure.

How does emptying water from a radiator act as an expansion vessel?

Expanding water will compress the air inside the rad, taking up the expansion. Come on, even the OP has managed to work that much out.

This is almost the same question as 'why are there diffferent sized expansion vessels in the world, can't we just use one size for everything?'

A larger system has higher water content and therefore a greater amount of expansion to take up, hence the need for a larger or additional expansion vessel. Again, basic stuff. I would suggest you talk less and think more before you make yourself look even more daft.

Expanding water will compress the air inside the rad, taking up the expansion. Come on, even the OP has managed to work that much out

No, fair enough, I don`t pretend to be a gas fitter nor plumber so if you feel a little wounded from our last encounter I understand, but my understanding of combi`s is that they are mostly sized on hot water requirements, this being the case, they are normally hugely oversized kilowatt wise for heating capacity and more than capable of taking a lot more radiators, why the need for an expansion vessel, I ask because i don`t know.

Expanding water will compress the air inside the rad, taking up the expansion. Come on, even the OP has managed to work that much out

No, fair enough, I don`t pretend to be a gas fitter nor plumber so if you feel a little wounded from our last encounter I understand, but my understanding of combi`s is that they are mostly sized on hot water requirements, this being the case, they are normally hugely oversized kilowatt wise and more than capable of taking a lot more radiators, why the need for an expansion vessel, I ask because i don`t know.

OK fair enough, I'd assumed from your previous posts before this thread that you were at least a plumber. Well, now you know why anyways...

Incidentally then, as you're not a gas engineer or a plumber, can you tell me where it says that it is a requirement that gas pipes in walls are protected by a metal plate? Because I still haven't found it...

Why would one have to add an expansion vessel to add new radiators? How would draining a radiator act as an expansion vessel?

In case it hasn't been answered.

The expansion vessel is size for 10% of the system water volume, adding extra radiators can push you over the limit, so you need a bigger or additional expansion vessel.

OK fair enough, I'd assumed from your previous posts before this thread that you were at least a plumber. Well, now you know why anyways

Not really, maybe you can explain why most combis sized on hot water requirements, mainly for hot water flow rate, are oversized regarding the heating requirements? surely this combi mentioned should be able to take a couple more radiators without the need of an expansion vessel?

Or are you the one looking a bit daft.

The expansion vessel is size for 10% of the system water volume, adding extra radiators can push you over the limit, so you need a bigger or additional expansion vessel.

Yes, but aren`t combis oversized generally to suit hot water requirements? so adding a couple of rads to an an existing oversized combi won`t make a difference, aren`t they normally installed to take into consideration extra rooms being added etc?

Incidentally then, as you're not a gas engineer or a plumber, can you tell me where it says that it is a requirement that gas pipes in walls are protected by a metal plate? Because I still haven't found it.

Can`t understand everyone`s hostility, not trying to prove anyone wrong, just trying to help out with my limited knowledge, not trying to undermine anyone, giving information as I understand it, If I`m wrong, by all means correct me, I don`t intentionally give out incorrect advice unless I have been given wrong advice. As for you Muggles regarding gas pipes in walls, consult a gas fitter,it`s correct, sorry.

OK fair enough, I'd assumed from your previous posts before this thread that you were at least a plumber. Well, now you know why anyways

Not really, maybe you can explain why most combis sized on hot water requirements, mainly for hot water flow rate, are oversized regarding the heating requirements? surely this combi mentioned should be able to take a couple more radiators without the need of an expansion vessel?

Or are you the one looking a bit daft.

This oversizing relates to the heat output, not the water content of the system, and in any case we don't know what the OP's original heating setup was, it would appear from the problem and temporary solution that it was close to the limit for the expansion vessel fitted, and the addition of four extra heat emitters, with associated pipework and additional water content, has taken it over the limit, hence the need for an additional vessel.

I'm not familiar with Aristons, having never fitted them, but I do know that some boiler manufacturers will suggest or specify an additional vessel for systems over a certain size as the one integral to the boiler is insufficient.

Incidentally then, as you're not a gas engineer or a plumber, can you tell me where it says that it is a requirement that gas pipes in walls are protected by a metal plate? Because I still haven't found it.

Can`t understand everyone`s hostility, not trying to prove anyone wrong, just trying to help out with my limited knowledge, not trying to undermine anyone, giving information as I understand it, If I`m wrong, by all means correct me, I don`t intentionally give out incorrect advice unless I have been given wrong advice. As for you Muggles regarding gas pipes in walls, consult a gas fitter,it`s correct, sorry.

No hostility intended, I was simply asking where you'd seen this so that I could use the book/document/whatever for my own education, as it obviously contains information I am not aware of. In the 'Installation of Pipework and Fittings' section of the Corgi Essential Gas Safety manual it makes no mention of metal plates as far as I can see, hence the question...

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