For pipe insulation on a heat-pump, the materials cost isn't significant compared with the energy savings.

I'd recommend the closed-cell elasomeric nitrile-rubber stuff which is commonly used by refrigeration specialists.
BES.co.uk sell the Kaiflex version.

For insulating around valves, there are Kaiflex options for 42mm internal bore and 54mm.

Armaflex is another brand of the same material. Both companies offer sticky-tape rolls which are used to lap across joins.

To insulate the external pipe-runs to a heat-pump, choose insulation marked for "solar".

At the heat-pump end it needs completely sealing to avoid rain entering between pipe and insulation.
You can use an external mastic as you fit the insulation. CT1 or Plumbers Gold (from Toolstation) are suitable quality mastics with excellent adhesive properties.

At the other end of the external pipe-run, the insulation should cover the pipe right through the wall and into the house.

@transparent again spot on and I would be oblivious to this otherwise. The installers are coming back to fit more batteries so will purchase some 95 mm² cables ready for the change and asking for the MCS accrediy. Meanwhile I'll crack on with DNO - they've been good enough to me by installing the 3 phase for free

To get suitable 'low voltage'/high-current battery cable by the metre, try 12-volt Planet or Split Charge (who also sell on ebay).

You also need the right size of ring-style crimp connector.
For the SunSynk 3ph inverters these are held by an M10 bolt.

In the UK, ring-terminals are marked with the cable-size in sq.mm and the bolt-size in mm.
So SC25-10 is for a 25mm² cross-sectional diameter cable with the ring suitable for a 10mm diameter bolt.

@bretix  I don't think there's anything particularly unusual about the pair of GSL batteries you have.

I'm unsure if it's a "current model" because there are some suppliers offering ex-demo versions at lower prices, including ITS here.
That's often occurs when a later model is launched.

I assume ITS was your installer because they have a photo of your particular installation on their site here.

It's a very standard configuration of 16-cells in series using LiFePO4 battery chemistry.
There's an in-built Battery Management System (BMS), which you have communicating with your SunSynk inverter.
But I suspect it's only linked in order to show the battery state on a SunSynk app.

A BMS doesn't have to be directly connected to an inverter with a data-cable.
It will quite happily get on with protecting your cells from under/over-charge on its own.

You can increase your storage capacity by adding your own 16-cell LiFePO4 self-assembled batteries in parallel.

I've built LiFePO4 batteries on steel shelving, such that they're still visible;

But if you'd prefer to have them in a steel case, then have a look at Fogstar online.

They offer the Mason boxes, manufactured in China by Seplos, and discussed here on this forum,
or their own Fogstar battery enclosure, which can accept cells of slightly greater capacity.
Each contains the BMS and wiring. You just add the LiFePO4 cells and wire them up according to the instructions.

These large-capacity battery enclosures have to be DIY assembly because they weigh over 110Kg when loaded with cells.
You first place the box where you want it to be located, and only then add the cells one at a time!

As you can see, the cost per kWh plummets once you're not paying someone else to assemble the battery in a factory,
and then an installer to connect it on-site.

@transparent again thank you you have been really helpful and informative and given me a couple more projects to get sorted along the way .

This hub is brilliant and has such a helpful community. Lugs and cable ordered . New lagging and proper cutter to follow . Now what to do with the gaping hole left in my garage wall !

@bretix I spent ages on here with my train wreck installation.  It’s not altogether what you see but what’s hidden, like under the floors etc. I locked swords with my installer who insisted my heating was perfect so I got samsung out and they condemned it.  It was so bad the pipework had to be all removed and reinstalled.  As with mine they run the pipes through the wall with no insulation where there is a through the hole kit that should have been fitted.  I had only 3% antifreeze, wrong size of pumps, wrong size of piping, plastic piping etc etc  and it took them longer to repair it than the initial install. So whilst you still have a guarantee check everything.

@david999 the company that installed it a year past January have since gone bust. I've still got warranty with Grant and it was MSC verified but don't think I can do anything without cost.

There was a rival company (Elite) who I wish I'd gone with at the time who are still going very strong.

@transparent correct they were purchased from ITS but installed by a regional company. 

I never knew you could mix the batteries. The fogstar looks good but building my own add ins looks like another good DIY project😄

@bretix when samsung came out to me they said if anything goes pop they won’t cover the repairs so it had to be all rectified. It was very expensive to get the engineer out but I claimed it back from my installer.

@david999 thing is I had it serviced by a grant engineer last October and was told it looked a good installation!

Posted by: @david999

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they said if anything goes pop they won’t cover the repairs so it had to be all rectified.

Really?

Like... er... WOW!

And I'd always thought they ran on AC

@transparent Don’t you think that that is a bridge too far? 😉 Toodles.