And we are now back down to 7.2lpm but heating is still going 

If removing that strainer made a difference, then it's possible that something has become dislodged within the pipework.

We can't tell if that 'something' was an object within the body of the strainer,
or possibly elsewhere, and that the sudden loss of flow has moved it.

Equally, you will definitely have introduced fresh air by opening the strainer,
and that will require purging from the various release-valves over an hour or two.

So, looks like it might be an incorrect sizing of primary pump. The installer (who was the subcontractor to who I used) came out and advise he was never given the heating design by the company who contracted him despite asking multiple times.  When installing he pointed out that there was no primary pump ordered so the main contractor went and purchased one (the Evosta 3 60/130).  What the installer and I think has happened is the main contractor has seen the price difference between the 60/130 and the 80/130 and went for the cheaper 60/130 (without actually understanding what those values mean).

I am in the process of requesting the full heating design (they did come out and survey everything) which brought them to the conclusion of not needing any new radiators and an 8kW system.  Will let you all know how I get on.

P.S We also notice that even when the heating wasnt on, the secondary Grundfos pump was still running which seems to make the radiators cool down super quick if it's still pumping the water around and the ASHP isnt heating it.  When we set DHW to on, the secondary pump goes off.  Is this normal or has some mis-wiring occured?

Thanks

@netdonkey The primary pump should stop after a while when there is no DHW or Heating demand, it may have an overrun to dissipate the small amount of heat left over but I am sure this is only for 30s on some systems. This pump should also be wired through the ASHP control and not on an independent supply with a switch on the wall.

To add, the primary pump also can run for a while before the system fires up to confirm flow.

Posted by: @ashp-bobba

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@netdonkey The primary pump should stop after a while when there is no DHW or Heating demand, it may have an overrun to dissipate the small amount of heat left over but I am sure this is only for 30s on some systems. This pump should also be wired through the ASHP control and not on an independent supply with a switch on the wall.

 

So the primary pump ( EVOSTA 3) does this, only comes on when required.  The secondary pump which is at the bottom right of my setup picture which is attached the the flow towards the radiators is on all the time.

Going to trace where it goes on the MIM 

@netdonkey OK, so this Grundfoss pump should only turn on an off when required in heating mode as your system runs through a buffer, there will be some form of stat that controls this, its should ideally through the ASHP controls if you are using their smart controls linked to a main stat, or through the ASHP control when engaging heating mode which can also be via a 3rd party stat or controls. So it depends how they have set up your system.

@ashp-bobba -  any chance of a diagram please?

Pencil on the back of an envelope will do!

@transparent 

Pretty much like this but the cylinder and buffer are combined in the same unit.

@netdonkey Primary pump should run as follows:

Heating demand on 

DHW demand on 

Defrost demand on 

Secondary pump should run as follows:

Heating demand on 

Defrost demand on (only of the volume of the buffer is not enough for the min volume for the ASHP to defrost)

Do all ASHPs have that Primary Pump inside the building?

Or is it sometimes within the external heat-pump / heat-exchanger unit itself?

@transparent Both, Mitsubishi is inside, Samsung is in the Monoblock unit