It is difficult to identify from a photo what task each vessel is performing, but the ones in question look more like expansion vessels rather than volumiser or buffer tank.

Can you provide a close-up photo of the nameplate on each device?

Hi Derek, 

Thanks for taking a look.

 This is the one on the right hand side. 

There is no label on the white vessel on the left but it looks to me as if it is probably this:

UNVENTEDCOMPONENTSEUROPE.COM "https://www.unventedcomponentseurope.com/vaillant-spare-0020009861-18-litre-potable-expansion-vessel.html"

Vaillant Spare 0020009861 18 Litre Potable Expansion Vessel - Unvented Components Europe, Unvented Cylinder System Spares, Spares for Hot Water Systems, Plumbing & Heating Parts - Specialists in plumbing & heating spares

(Ignore the second photo)

The grey one in the middle doesn't have a label but I think I remember seeing a box with 25L buffer vessel written on it somewhere. 

Don't know if that helps at all?

Best,

Rob

@rob-k

The vessel with the nameplate would appear to be the following, which may be being used to add volume to your system. Is it connected within the pipework from your heat pump.

SPATEC.CO.UK "http://www.spatec.co.uk/shop/viewitem.php?productid=680"

Spatec NI Ltd online store

Spatec are one of the UK's leading suppliers of plumbing, heating and ancillary products. Discover our range of plumbing and heating products, including Zip Hydrotaps, Hydroboils, filters, valves, expansion vessels etc

The white and grey vessels appear to be expansions vessels for the primary and secondary water systems. Their purpose is to allow expansion and contraction of the water within the systems due to change in temperature. They should both have a nameplate which may be round the back or on top.

After having a closer look at your original photo, I think that your system is piped up as follows:-

The pipe coming through the floor furthest on the right would appear to be the flow pipe from your heat pump. This feeds up to the tee where it branches via the horizontal pipe to the electrically operated 3 port valve.

The vertical pipe coming out of the top of the 3 port valve connects to the heating coil within the hot water cylinder. The return pipe from the heating coil connects to a tee near the base of the hot water cylinder.

Pipework from this tee is connected to the bottom connection on the volumiser tank. The top connection on this tank is connected to the return pipe to your heat pump via the filter unit. The outlet from the volumiser tank is also connected to the grey expansion vessel.

The bottom port of the 3 port valve is connected to the flow pipe to the heat emitters and disappears into the floor. The return pipe from the heat emitters connects to the tee feeding back to the heat pump via the volumiser tank.

The mains water supply is via the left most pipe coming through the floor. This feeds into the Pressure Reducing Valve (PRV), after which there is pipework connected to the white expansion vessel and also to the bottom of the hot water cylinder. The pipework feeding out of the hot water cylinder is mounted on the top.

To decide whether to remove the volumiser tank or not, you would need to calculate the volume of water within your heating system, and confirm that this volume is greater than the minimum volume specified in the heat pump manual. Leaving the volumiser in place should not be too detrimental even if it is decided that it is no longer required.

Thanks for the run through Derek. So it seems as though it's in the correct position? I think I'll leave it in place and add a bit of insulation around it.

Had a look a the min system volume for defrost cycle for the Arotherm 7kw and it's 55L. I believe our heating system is over 130L so it does seem as if the volumiser is over kill.

@rob-k 

I know it’s a while ago, but Derek is right all is piped as he say, and is OK. A bit of insulation on the pipes wouldn’t go amiss though. 

@wobby1 thanks for this - yes his advice was reassuring and system is working very well. I was a bit worried after loads of people had pointed out issues with the install on a Facebook group so I thought I would double check on here. Piping has all been lagged now too.

@rob-k 

You’re very welcome and it’s really good to know it’s all working well. Just shows that when heat pumps are installed correctly they do work and work well. 
regards 

Posted by: @rob-k

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@wobby1 thanks for this - yes his advice was reassuring and system is working very well. I was a bit worried after loads of people had pointed out issues with the install on a Facebook group so I thought I would double check on here. Piping has all been lagged now too.

I do believe that the 'knowledge' level on facebook can be a dangerous thing. 😋 

The bypass is not installed correctly, as it should incorporate the volumizer, which it doesn't.