How to fit an external expansion vessel ?

[bluefudge11]

Hi all, this is my 1st post so hopefully i have not messed up

my combi boiler expansion vessel is shot so i want to fit an external one .
The boiler has Pressure Relief Valve, filling loop and gauge so i'm assuming i can just plumb a new vessel in to the CH return without having to use another PRV, gauge and filling loop?

It will be fitted close to the boiler

It is a sealed system - using Baxi 105e combi

Help and advice greatly appreciated
Thanks
BF

 

[Agile]

I have never done it on that model but there is no reason why you should not fit an external EXV.

Doing that will even give an extra hot "instant" storage capacity.

You dont need to fit anything else as long as you are aware that the boiler isolating valves could be closed and isolate the protective devices in the boler.

To guard against that it would be necessary to fit a PRV close to the new EXV.

You should not fit an isolating valve in series with the new EXV ( although it does make maintenance so much easier and I would often fit a tool operated valve but its not correct ).

Tony

 

[Master of None]

Doing that will even give an extra hot "instant" storage capacity.

You dont need to fit anything else as long as you are aware that the boiler isolating valves could be closed and isolate the protective devices in the boler.

To guard against that it would be necessary to fit a PRV close to the new EXV.


Tony

Not having a dig Agile. But.
Surely the water in the EXPV is static and therefore its heat will not contribute to the system at all.
Under what circumstances would you get an over pressure event in a system isolated from the boiler?
As you say I would always design in a valve (lockshield) to isolate an expansion vessel and drain cock to enable changing/charging EXPV without draining system.

 

[Agile]

Surely the water in the EXPV is static and therefore its heat will not contribute to the system at all.

You may well be right.

However he first posted about his problem by hijacking a topic about a 105 Instant. Many posters dont bother to tell us that their boiler is an instant. So I thought its more likely to be an instant but it may not be of course and the advice he was asking did not have any impact on which model it was.

So if its an instant then it increases storage capacity and if its not then it does not.

Tony

 

[ddk]

yeh you could easily put an external expansion vessel in the system. go for a 6/8ltr brefco external vessel. you will need a 3/4 to 22mm female BSP fitting to fit the top of the vessel, then you can either tee it straight into the flow/return pipe or reduce the 22mm pipe to 15mm and use a 15mm compression tee-piece and fit that in after the non-return valve of the filling loop

 

[muggles]

go for a 6/8ltr brefco external vessel

That's a very bold statement considering you don't know the size of the OP's system...consider the possibility that the original EV broke because it was too small. Much better to find out the actual requirements rather than guessing

 

[ddk]

considering a 6/8 litre vessel charged to 1bar pressure is suitable for 75 litres of water content in a system I am sure it will be more than enough for most domestic systems, especially one ran off a bog standard 105

 

[swbjackson]

Have a look at http://www.rwc.co.uk/content.aspx?page=ABOUT_EXPVESS for guidance on sizing.

 

[Agile]

Thats a bit of overkill suggesting an 18 litre EXV for a 32 kW boiler! But of course they make them dont they!

If you see what combi makers use then its usually a 6 litre for 24 kW and an 6 litre for a 32 kW.

Of course they correctly say that if the sys volume exceeds 75 litres an additional EXV is needed.

So a 6/8 litre would be what the combi makers use and suitable for an average three bed semi with pressed steel rads.

Often forgotten just how much water the cast iron rads hold.

Tony

 

[kevplumb]

can you oversize an expansion vessel

 

[Slugbabydotcom]

Screwfix is a good place to get them from but the bracket is listed elsewhere in the book. A 12 litre is not much dearer than an 8 litre and will cover most heating systems easily so go for that unless space is an issue. Remember an 8 litre vessel has already gone wrong !
Its 3/4 Male Iron coming off the vessel so i suggest you get a 15mm X 3/4BSPF connector for it. I fit an isolation valve in line to allow future work on the vessel.

 

[BigBurner]

I have never done it on that model but there is no reason why you should not fit an external EXV.

Doing that will even give an extra hot "instant" storage capacity.

You dont need to fit anything else as long as you are aware that the boiler isolating valves could be closed and isolate the protective devices in the boler.

To guard against that it would be necessary to fit a PRV close to the new EXV.

You should not fit an isolating valve in series with the new EXV ( although it does make maintenance so much easier and I would often fit a tool operated valve but its not correct ).

Tony

What the hell is this one babbling about?

His CH expansion vessel is shot. He can cap the old off, and tee into the return near the boiler and fit another. It is so simple. Just put an in-line isolator valve to remove the vessel in future. Size the vessel to suit.

 

[twgas]

His CH expansion vessel is shot. He can cap the old off,

not if its the "instant"

 

[Agile]

Big Burner has not looked at the brochure for the 105 Instant so he knows nothing about them!

Tony

 

[BigBurner]

His CH expansion vessel is shot. He can cap the old off,

not if its the "instant"

Yep. Combined expansion and DHW storage vessel.