Unvented Cylinder Expansion Vessel - advice sought

[David C]

Hi,

I am a homeowner, I had a new unvented cylinder (OSO DC 300) fitted in August, and had a small problem yesterday with the pressure valve dumping water and making a lot of noise. Eventually this was resolved. However, during my conversations with plumbers it appears that I have a red expansion vessel rather than a white or blue one!.

On investigation, it appears that although my cylinder came with a white one, my gas safe heating engineer saw fit to install a different one.

Is this a problem I should have fixed? My 'google' research suggests that the difference is that the red ones are not potable. I am not sure how much of a problem this is.

David

 

[fezster]

Is the red vessel definitely connected to your mains water supply and not to your central heating system?

If so, it should still function to take up the expansion of hot water - so the fact your Pressure Relief Valve is opening suggests it is either defective or has not been charged correctly (or may even be too small).

The use of a non-potable vessel means that it will disintegrate much sooner. It may also be against the water regulations - someone more knowledgeable will be able to confirm.

 

[David C]

HAHA! This is the question everyone asks! Yes DEFINITELY!

Is the red vessel definitely connected to your mains water supply and not to your central heating system?

 

[David C]

If so, it should still function to take up the expansion of hot water - so the fact your Pressure Relief Valve is opening suggests it is either defective or has not been charged correctly (or may even be too small).

So, this is a good question. My mains pressure is very high, and there is a valve that 'reduces' it.

Once I got in touch with the installer, he talked me through adjusting the valve to lower the pressure to 2.5 bar and it seems to be fine. I guess my concern is what had changed, given it had worked for weeks with no problems.

 

[fezster]

Depends on the pre-charge on the vessel. It should be set to whatever your incoming mains supply is reduced to (and this in turn should be set to whatever your cylinder manufacturer has stated).

The idea is that no water enters the expansion vessel at normal reduced mains pressure. Only when the hot water is heated is the expansion taken up by the vessel.

 

[Best]

This is weird! Your installer fits a different vessel to the one supplied and then advises you over the phone to adjust the inlet pressure ????
Get an unvented qualified plumber in immediately to check and test the work.
I would doubt if it is safe by your description.
Could you put some photos of cylinder, vessel and pipework?

 

[ShaunCorbs]

Any pics of the install?

 

[David C]

Its a bit of a pita at the moment.....see if this helps

 

[David C]

I have also ascertained the vessel that came with the cylinder was an RWC ARB24, it is white -🙂 and 24l rather than the 18l

 

[ShaunCorbs]

I can tell you now it's not fitted right

 

[David C]

Could you elaborate please? what is wrong?

 

[Best]

Contact the unvented unit manufacturer technical and send them some good photos showing the pipes and vessel clearly.
If that vessel is for a sealed heating system, then it will rust through and flood your property with mains high pressure water.

 

[ShaunCorbs]

Also the safety discharge isn't correct

 

[David C]

I am going to get it replaced. And as part of the replacement get a verification. However, I would like ShaunCorbs initial view

 

[David C]

Ah just saw his response about the safety discharge Thanks

 

[Best]

Could you elaborate please? what is wrong?

You said yourself the vessel was replaced and by a red smaller vessel

I am going to get it replaced. And as part of the replacement get a verification. However, I would like ShaunCorbs initial view

It is wrong, simple as that. Your installer is responsible for the cost to put it right.
Discharge pipes all must be above the tundish also.
Normally I would say get the plumber back, but not with that job.
Just get the manufacturer to condemn it and you have all the proof that you need before you contact the installer.

 

[David C]

Ok Many thanks all for your help

 

[SimonG]

Is that overflow pipe for the discharge?

 

[ShaunCorbs]

Is that overflow pipe for the discharge?

Yep 😀

 

[SimonG]

Oh dear.

 

[Best]

Plumber is going to be made look silly.

 

[David C]

Are you talking about the discharge from the cylinder or from the expansion vessel?