Combi expansion vessel

[nrh]

I am making advance preparations to replace the expansion vessel on my Vaillant combi, and wondered if some kind pundit would kindly advise on what to expect. :-)

Obviously I will need to remove the combi from the wall first to get at it, but my question relates to the actual method of connection to the water union. Looking at the new part, I cannot see any form of threading, either internal or external. Instead, it is quite smooth inside the connection orifice with only a circular rubber 'o'-ring visible about a centimeter or so inside set into a groove. (See pic here)

this mean that the vessel is simply a male to female-type push fit onto the connection pipework? And to remove the old one, will I only need to unscrew the locating bolts on the main framework, in order to pull off the old vessel? Finally, when reconnecting, should I use a silicone grease or similar on the 'o'-ring or elsewhere?

Any other helpful hints gladly accepted.

Kind regards

Nigel

[Tony Bryer]

You may have already ruled out this possibility, but if the existing one is not leaking can you just tee an external one in at some suitable point on the system? Generally much easier and cheaper.

[sponix]

If it ain't sprung a leak I believe you can add one elsewhere in the system.

Someone else will be able to advise whether it should be connected in the flow or return (I suspect flow)

sponix

[nrh]

In news: [e-mail], Tony Bryer scribed:

Tony, thanks for responding. However, I have already bought the new one, (see the pic) as the old one is leaking. It does not hold pressure for longer than a couple of days at most, and a tee-off would not work. I have already got an emergency-type setup in place using an existing rad as a makeshift expansion vessel, and even that still needs some topping up, although *much* less frequently. :-)

Any tips on how they plumb in though, would be much appreciated. ;-)

Cheers Nigel

[nrh]

In news: [e-mail], sponix scribed:

Thx Sponix, but check my reply to Tony above.

Best Nigel

[nrh]

In news:XCvzf.3500$ [e-mail], nrh scribed:

Oh and btw, if I understand you correctly, what's the point of adding on an additional expansion tank, if the existing one is working ok (i.e. "ain't sprung a leak")? :-?

[Andrew Gabriel]

I don't know that boiler, but I suggest you check the service instructions. I would be rather surprised if changing a pressure vessel requires removing the thing from the wall.

[Set Square]

It rather depends on what *sort* of leak it's sprung!

An expansion vessel contains air and water, separated by a diaphragm. When the water in the system expands, it compresses the air a bit more - with the air providing a cushion to prevent excessive pressure increases.

If all the air leaks out, the vessel fills completely with water, and there's no longer a cushion. In this case - assuming that simply topping up the air via the Schrader valve doesn't fix it - it's perfectly feasible to 'abandon' this vessel and fit another one elsewhere.

Only if the old one is leaking *water* to the outside world does it definitely have to be replaced.

[sponix]

It could have a leaky diaphragm, ie it doesn't wotk but it isn't leaking water to the outside.

If it's leaking water you have no option but to replace.

sponix

[sponix]

The wonders of usenet propagation will never cease to amaze!

sponix

[Ed Sirett]

I take it you have read the FAQ. Yes the Vaillant in common with many boilers does not make exchanging the vessel an easy job. Although the latest models have changed this.

Generally the ones internal to a boiler are very often connected with an

8mm microbore type pipe.

External units (Zilmet being a major manufacturer) usually have a 3/4" threaded connector although small units might be 1/2".

[nrh]

In news: [e-mail], sponix scribed:

LOL! Weeell, I didn't want to sound all stuck up and say 'I refer the honourable gentleman to the reply I made a moment or two ago'. ;-)

Cheers Nigel

[nrh]

In news:43ce9b21$0$87290$ [e-mail], Andrew Gabriel scribed:

Andrew, Yes indeedy. I do have to remove it. :-( Book says: "Disconnect.....(blah, blah, all gas and water connections)....Remove appliance from the wall. Remove 2 fixing clamps (Fig

80) Lift up and take out expansion vessel to the rear".

"Juz loik that!" :-)

Now that I have re-read that, I guess it has just answered my own question, at least in part. It seems that the thing just slips off (now where have I heard that before???) after you under the 2 clamps. Anyone wanna have a poke at any of that?

Nigel

[nrh]

In news: [e-mail], Ed Sirett scribed:

:-)

Nope. Mine is deffo not 8mm! Just done a quick measure of the internal diameter, and it looks like 3/4", although unthreaded, as per my pic.

As I stated in my reply to Andrew further down, the service booklet seems to state that the thing just 'lifts off' after undoing 2 clamps which hold it down. Normally, I would blithely accept that as gospel, but experience has now taught me that theory don't always match up with practice!! So, cynical as I am, I was wondering if the thing was unlikely to just 'lift off' and would I need to consider any other possibilities in that regard, such as buying in a supply of semtex or somesuch? Also, should I use a lubricant on the 'o'-ring when reassembling the new one?

Cheers and thanks all for your interest. Nigel

[Ed Sirett]

I'm not sure what the size of the internal pipe from the boiler innards to the expansion vessel is. The only one I've come across which failed I fixed by adding a vessel under the stairs.

The boiler manual shows the connection to the vessel as being threaded. My guess is that the seal is by a fibre washer rather than on the threads. The replacement vessel will probably come with a new washer.

[bof]

Unbled radiators would act like expansion vessels too, I'd have thought.

[Ed Sirett]

Yes but the radiator would not get hot at the top. Using a radiator or two is suggested in the FAQ as an emergency work around for a failed vessel.

[Roger Mills (aka Set Square)]

.

Also, it's not too easy to prime with a finite positive pressure when the system is cold.

[Ed Sirett]

That's not necessary. As the system is filled the radiator becomes pressured. Roughly half the rad will be filled when you are up to 1 bar.