External expansion vessel.

[5544]

Well, I have to go back to a heating job where the boiler expansion vessel needs changing,. For a number of reasons I intend fitting an external one. I am going to put it below the boiler using a half inch to 15mm adaptor, to 15mm then to a flexible hose to connect to the return to the boiler. Can someone remind me of the max length to the expansion vessel using flex. Yes I am gas safe registered, and yes I am self employed, but no one remembers everything. Kindest regards.

 

[Destroyer2813]

Y flexi just hard pipe it and havent most vessels got 3/4 threads on em

 

[5544]

Yes three quarter is right. Thanks

 

[dancinplumba]

Well, I have to go back to a heating job where the boiler expansion vessel needs changing,. For a number of reasons I intend fitting an external one. I am going to put it below the boiler using a half inch to 15mm adaptor, to 15mm then to a flexible hose to connect to the return to the boiler. Can someone remind me of the max length to the expansion vessel using flex. Yes I am gas safe registered, and yes I am self employed, but no one remembers everything. Kindest regards.

Really !! well i never

 

[AWheating]

what has gas safe or being self employed got to do with external expansion vessels?

i would pipe it in copper, chuck the flexi in the van. flexi's and heating temps dont mix well, even on the return.

 

[stoker122]

Hard pipe and make sure the valve can be accessed for charging. We look after several flats in a block, all the expansion vessels are fitted with the valve on the floor.
Only managed to persuade 2 landlords they should be repositioned.

 

[IND_Nick]

Just a quick question on this topic. What is the best practise with the failed internal expansion vessel. If it remains water tight does everyone just leave them be or should it be capped off inside the boiler?

 

[stoker122]

Screw down the dust cap and leave it there.

 

[boza]

dont use a flexy pipe they collapse inside after a short while
and leave the expansion tank in place

 

[MatthewHurt]

This may already be a little bit late - and a possibly misguided piece of advice.. But here goes anyways...

If you are choosing to fit a new/external expansion vessel mainly due to the assumption that the Diaphragm has split and is letting water through to the air side (Meaning the boiler keeps blowing water out of the PRP as soon as it heats up) - HOLD FIRE!

I must have changed about 5 or 6 of them for this reason before someone showed me just how much condensate can collect on the air side of a vessel (approximately half a builders bucket full).

You can make sure this is not the only problem by opening up a drain point (preferably below the boiler) with a hose attached and left hanging into a bucket etc.
Release all the air from the expansion Vessel (by pushing the Schroeder down)
Then attach your foot pump onto the vessel and pump it until water stops coming out.
Then replace the Schroeder valve (if required) and pump the vessel back up to about .8 bar

According to a Vaillant engineer I spoke to about it, expansion vessels almost never split and this (^^^) or a blockage on the pipe leading up to the vessel are the only problems that ever really occur with them.

Hope this helps (even if 5544 has already fitted the external one / if there was another reason for fitting) and I don't mean to teach anyone to suck eggs... It is just a bit of advice I've personally found extremely useful!

 

[stoker122]

Hi Matt,
How does the condensate push back through the diaphragm?
Surely this is just the diaghram expanding and pushing the water in the boiler out?

 

[Whn1]

This may already be a little bit late - and a possibly misguided piece of advice.. But here goes anyways...

If you are choosing to fit a new/external expansion vessel mainly due to the assumption that the Diaphragm has split and is letting water through to the air side (Meaning the boiler keeps blowing water out of the PRP as soon as it heats up) - HOLD FIRE!

I must have changed about 5 or 6 of them for this reason before someone showed me just how much condensate can collect on the air side of a vessel (approximately half a builders bucket full).

You can make sure this is not the only problem by opening up a drain point (preferably below the boiler) with a hose attached and left hanging into a bucket etc.
Then attach your foot pump onto the vessel and pump it until water stops coming out.
Then replace the Schroeder valve (if required) and pump the vessel back up to about .8 bar

According to a Vaillant engineer I spoke to about it, expansion vessels almost never split and this (^^^) or a blockage on the pipe leading up to the vessel are the only problems that ever really occur with them.

Hope this helps (even if 5544 has already fitted the external one / if there was another reason for fitting) and I don't mean to teach anyone to suck eggs... It is just a bit of advice I've personally found extremely useful!

I don't get it, how would that get the water out of the vessel?

 

[stoker122]

If condensation has collected on the air side of the diagram isolate the boiler and release the system pressure.
Recharge the vessel to 1 bar then completely deflate, this should expel the condense.
Recharge the vessel to 0.8 bar then fill up the boiler.:smile5:
I have also had plenty of diaphragms that have been stuck to the wall of the vessel, you can hear them peeling off as you pump them up.

 

[MatthewHurt]

That was exactly what i kept asking myself after the guy was explaining it to me, it doesn't seem to make sense that if the diaphragm isn't split that you can possibly push the condense back out.. and to be honest I still don't know!
- I will have to ask the Vaillant Engineer tomorrow!

But after having tried it for the last few months I have to say that it has actually worked every time, and each time I have been absolutely amazed at how much condense has come out!
Just try it next time you get one that seems to be split (it only takes 5 minutes, so its not a major problem even if it doesn't work)
I will call the guy back up tomorrow and ask though as the same question has stumped me as well!

 

[lame plumber]

if condensation is occuring on the air side, once the water comes out of that bit of air held then what theres no new air getting in or out!!! someone isnt thinking straight here!!!!!!!!!! better test, take burst vessel out, pump it up and listen to the hiss coming out the 3/4" connection as the air escapes out of the split diaphragm

 

[stoker122]

if condensation is occuring on the air side, once the water comes out of that bit of air held then what theres no new air getting in or out!!!

You what?

 

[lame plumber]

You what?

there is only a set amount of air under pressure in the top of an expn vessel that can only hold a set amount of water vapour that may cndense out of the air. so possibly a tiny puddle at most, thats wot ie the earlier comment about condensation is bs

 

[stoker122]

I think Matthew is getting mixed up between a small amount of condense and the amount of water that comes out of an isolated boiler when the E.V. is pressurised LP.

 

[lame plumber]

probably, but you never quite know what people think on here at times

 

[beesley121]

Someone's truly got their wires crossed here.

if water comes out of the air inlet valve, the vessel is knackerd full stop. There should never be water on the air side. Expansion vessels are filled using pure nitrogen to stop the diagram perishing prematurely so no moisture should be in there

 

[stoker122]

No nitrogen left after several years