So... after 2 frustrating years, with a COP of 2, for a house with underfloor heating and very good insulation, I finally found the issue (or issues)

1- the smallest issue, which generates a delta T of 1 or 2 - the "plumber" mixed the supply and return from the heat pump to the puffer... supply is in the lower part and the return on the higher part, when leaving the puffer they are in the correct place, supply is up and return is down... so... the water is really mixing in the puffer 😀 😀 - this issue i have not fixed yet, it's on my ToDo list

2. the BIG issue - the "engineer" (electropainter - explained below) who made the connections between the outside and inside units of the heat pump, did not do a proper job and was losing refrigerant since the beginning... a proper engineer came by yesterday and it seems i had no more refrigerant... now it's fixed and after 12 hours in cooling mode i have a COP of 6.... I have NEVER seen this COP on my heat pump, NEVER, maximum was 2.5, in the beginning...

I have no words, I don't know if I should laugh or cry...

There are 2 saying in romanian which fit my use case:

- what i learned recently: "I am too poor to be cheap" - i'll never work with cheap people, it will eventually cost you double or triple, better find competent workers which have a higher price

- "electropainter" handyman (in romanian - electrozugrav) - a guy which does something for 1 year, with no proper learning and is now advertising himself as a specialist.... thats with what specimens i worked initially...

I'll come back with an update again, after a few months.

I hope this helps others... don't make the mistakes I did, better pay more for a good worker (regardless for what) than go for the cheap ones and have to repair what they did, it will cost more!

Great news.  Lack of refrigerant will certainly degrade cop.

Posted by: @bubuontheweb

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1- the smallest issue, which generates a delta T of 1 or 2 - the "plumber" mixed the supply and return from the heat pump to the puffer... supply is in the lower part and the return on the higher part, when leaving the puffer they are in the correct place, supply is up and return is down... so... the water is really mixing in the puffer - this issue i have not fixed yet, it's on my ToDo list

I assume you mean buffer not puffer.   You are correct this will cause even more mixing than a correctly plumbed buffer!  Of course better still almost certainly is not to have a buffer at all.  I presume there is no way to pursue whoever installed this to take the buffer out or better still turn it into a 2 port volumiser.

If you are replumbing this yourself then there is an arrangement of valves you could add in to allow you to try it as a volumiser not a buffer, but be able to reverse the operation if for some reason it doesn't work.  Just saying if you are planning extensive work on plumbing.

@jamespa Buffer, yes 😀 

Volumiser, you mean to have it linked only to outlet or inlet? Not connecting them both, right?

I plan to do it myself, redo everything, without buffer. However, I plan to add some valves along the route in case removing the buffer does not give a better outcome. 

Wondering if someone could share a diagram on how it should look? And what should i share beforehand, as info, for this?

Read on a couple of pages from here 

https://renewableheatinghub.co.uk/forums/renewable-heating-air-source-heap-pumps-ashps/4p-buffer-tank-connections/paged/3/

That describes the configs.

With a volumiser you need also to bypass or remove the secondary pump 

Alternatively number ports clockwise starting top left.

For a buffer:

Flow in from heat pump = 1

Flow out to emitters =2

Return from emitters (via secondary pump) =3

Return to heat pump =4

Secondary pump can alternatively go between port 2 and emitters.

For a volunteer

Flow in from heat pump = 4

Flow out to emitters =2

No secondary pump

Tank bypassed on return

@jamespa I assume “volunteer” should be volumiser?

Posted by: @judith

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@jamespa I assume “volunteer” should be volumiser?

Autocorrupt seems to be working overtime.