Why internal combi expansion bladder fails?

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kez1

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Hi

I have a Grant Vortex 36e, 36Kw keroscene combi boiler, used to heat the house hot water and radiators. I got it in 2008, so it's 8 yrs old now.

It has worked flawlessly except that I have had to replace the internal expansion vessel once before and now again (twice in all).

I just pressed the Schrader valve on on the vessel and water came out so it's bust.

Here is the like for like replacement that is now on it's way to me.
http://buyplumbingonline.co.uk/products/Zilmet-14Ltr-Expansion-Vessel-531{47}L.html

On occasion I think the system has been pressured to 2 bar cold, but never more.

Anyone any ideas why I have had to replace these twice.

ps there is another expansion vessel on the system. Just tested it and air comes out when the schrader valve pin is pressed. It's been in there since the (above mentioned) Grant combi boiler was installed. Why would the boiler internal expansion vessel go bust but not the external circuit one?
 
How much does system pressure increase from cold to hot.
How much precharge is in the vessels. What size is the other one.
 
How water circuit has no expansion vessel.

Heating circuit has two expansion vessels.
These two are:
  • Zilmet 14Ltr Expansion Vessel 531/L pressurised to 1 bar which for the second time has failed

  • Attached photo of fitted cylinder. ~height is 27cm a radius ~12cm giving a volume of 12 Litres. It is always seems light as a feather, when I put my hand underneath it, even when system is hot.
  • Terry: I will have a look out this evening for system pressure increase from cold to hot. I will also put a car foot pump on the expansion vessel with air in it for current pressure (picture below) and let you know.
20160519_093036.jpg
 
That unit is for hot water
Heating expansion units are red
It's also fitted upside down the air gap should be at the top
 
steve32 said:
That unit is for hot water
Heating expansion units are red
It's also fitted upside down the air gap should be at the top
Click to expand...


Would you believe that that is the correct way to fit them?
 
There's a Skool of thought that a Potable expansion vessel should be inverted on an unvented cylinder. Thus reducing noise. A Potable (white) expansion vessel can be used on a central heating system, while its great on pressure, which is set 2-3Bar on hot water systems. I'm not so sure how well it'll take the higher temperatures??!!!

You can get some water out an expansion vessel Schraders valve, this can be a wee bit of condensation on a perfectly good vessel. A 'flooded' vessel can be the result of a knackered bladder, faulty Schraders valve or just needing to be pumped up. Always best to drain water from the vessel when pumping up. I always like to disconnect them - thus ensuring they're completely drained & it's easier to check for a f.cked bladder or Schraders valve.
 
kez1 said:
Hi

I have a Grant Vortex 36e, 36Kw keroscene combi boiler, used to heat the house hot water and radiators. I got it in 2008, so it's 8 yrs old now.

It has worked flawlessly except that I have had to replace the internal expansion vessel once before and now again (twice in all).

I just pressed the Schrader valve on on the vessel and water came out so it's bust.

Here is the like for like replacement that is now on it's way to me.
http://buyplumbingonline.co.uk/products/Zilmet-14Ltr-Expansion-Vessel-531{47}L.html

On occasion I think the system has been pressured to 2 bar cold, but never more.

Anyone any ideas why I have had to replace these twice.

ps there is another expansion vessel on the system. Just tested it and air comes out when the schrader valve pin is pressed. It's been in there since the (above mentioned) Grant combi boiler was installed. Why would the boiler internal expansion vessel go bust but not the external circuit one?
Click to expand...

Oil combi/system boilers always have grossly undersized expansion vessels.
 
Hi Folks

I was on the way out to the garage this morning to check the heating circuit system pressure, before doing a test for pressure difference between hot and cold.
Before I could do so I had to re-pressurise the system minimally, to 1 bar, as the pressure had fallen to almost zero. As I was doing so I noticed that water started dripping from the edge of the (bust) red Zilmet pressure vessel.

The new (boiler internal) Zilmet (replacement) had arrived the day before yesterday so I decided it was necessary to make the replacement straight away. Replacing the internal expansion vessel is very easy on this boiler.

After replacement I pressurised to 1.2bar cold and after running for 5 mins the hall radiator was hotter than it's been in some time. The hot system pressure is 1.6 bar.

Is this pressure difference too big. Do I need more expansion capacity.

Should I replace the white shown vessel above (approx 12 litres, air comes out when I momentarily press the schrader valve), with new red one? House has 15 rads.

Is it possible the white one is bust even though air comes out of the valve.
 
You needed to check the reading when system is completely cold and when all the radiators are at maximum temp. You should have set the internal pressure of the expansion vessel at 1.0 bar and have filled the system to 1.0 bar pressure. Once the heating has reached max temp the pressure should not have risen above 1.5bar. With 15 rads you would normally need an expansion vessel of between 18 and 24 lt for a grant combi. They have recently realised that many installers fail to calculate this and now,install 24lt expansion vessels as standard
 
I have the 26e external combi in 2010 and got through 2 expansion vessels in a couple of years, luckily I actually took out a 5 year warranty...however I was furious when it failed the 3rd time after being away on holiday during a cold spell at home and the house was freezing. Same old problem, zero pressure.....no apparent leaks. So I wrote a slightly scathing review of my Grant boiler on Boilerjuice's forums and very quickly Grant replied, contacted me and got an engineer to visit and add an additional expansion vessel inside the boiler (there's just a bit of spare room at the back end side) - since fitting this very slim extra vessel the thing has stayed pressurised and working for several years whereas it used to drop pressure every 6 or 9 months. Grant did all this for free by the way.

The Grant engineer said it wasn't uncommon to happen, depends on how many rads, how much expansion is in your pipes and rads......The power of forums, especially a concise, not too rudely written review of course.
 
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