Samsung Controller readings are House temp 22.3  outside -0.3 33.4 rising as bath run , water 23.5 . 
Readings in Loft Flow out to CH 37.9c back in 24.4c  From Hp 42.8 Return to Hp just before zone valves changed to DHW Replenish as bath run 34.9c Hope that helps ! 
Oh weather Station says -1.3 Indoor 22.9c to 23.3c indoors

The Samsung controller has information on the panel I thought might be relevent to mention so it said that the House temp. was 22.3c

The outside temp at that time on the controller said -0.3c

Circulation temp was 34.9c slightly lower than normal , but a bath had just been run. Hence the DHW was 23.5c

I read the circulation temperatures of the CH in the loft before the zone valve changed to DHW.

So the flow out to the CH system was 37.9c , the return temperature was 24.4c (quite low return)?

The speed was turned down at those figures above.

The flow temp. from  Heat pump was 42.8c

The flow temp. returning to the HP was 34.9c.

The House temperature on a separate Thermometer was 23c.

I hope I have explained that better!

I will try and find HP pump flow speed , its not in manual.

Perhaps the information is on here, it mentions on the comissioning sheet the circ speed should be three on the pumps , it has been on that upto a week ago , main out put is three , the others are two .

On the grounds that turning the pump speed down didnt help I would put it back up again.  Slow flow = higher deltaT across radiators = higher FT needed = lower efficiency.  If turning it down had helped with buffer mixing then it might have been worthwhile, now we know that this is not the case best to turn it up again.  Once you do can you remeasure the temps (flow to/from radiators).  Explanation now much better, high deltaT across rads a concern but lets see what reinstating the pump speed does.

@jamespa I have been up to change the CH pump and return pump back to No.3 and taken a note of flow temps circulating the CH . I will take another read later

OAT -2C 

Output to RADS 37.9C Return 24.4c

Flow from HP 42.8Cc Return to HP 34.9c

So deltaT across rad circuit  =  37.9-24.4 = 13.5C.  ~5C is what we are looking for.  So Im expecting the return from rads to be more like 32C than 24C

Either something is wrong with that measurement or you have a real problem (blockage) in your secondary circuit which will be costing you a further 15% penalty on top of the 15% penalty caused by the buffer tank.

Are you sure that the secondary is fully open except for any adjustments to LSVs to balance the radiators (with at least one LSV fully open)?

Are you sure about the measurement, particularly the one measuring 24.4?

Are you sure you took this measurement when the secondary pump was on and the system hadn't just come out of a defrost?

Are you sure that the 22mm becomes 28mm after a few metres?

This is, unfortunately, another reason to hate buffers, they deprive you of the tools to diagnose faults easily. 

please respond with any other information/measurements you have which might help unravel this.

Posted by: @jamespa

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So deltaT across rad circuit  =  37.9-24.4 = 13.5C.  ~5C is what we are looking for.  So Im expecting the return from rads to be more like 32C than 24C

Either something is wrong with that measurement or you have a real problem (blockage) in your secondary circuit which will be costing you a further 15% penalty on top of the 15% penalty caused by the buffer tank.

 

Are you sure that the secondary is fully open except for any adjustments to LSVs to balance the radiators (with at least one LSV fully open)?

Are you sure about the measurement, particularly the one measuring 24.4?

Are you sure you took this measurement when the secondary pump was on and the system hadn't just come out of a defrost?

Are you sure that the 22mm becomes 28mm after a few metres?

 

This is, unfortunately, another reason to hate buffers, they deprive you of the tools to diagnose faults easily. 

please respond with any other information/measurements you have which might help unravel this.

 

I will check return flow temp 24.4. 

System not circulating at the moment to measure properly , but will once it does. At present its 30c out and 22.8 return on CH

Not sure on whether it was defrosting late last night at the time of measurement, will catch up on that.

Posted by: @jamespa

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On the grounds that turning the pump speed down didnt help I would put it back up again.  Slow flow = higher deltaT across radiators = higher FT needed = lower efficiency.  If turning it down had helped with buffer mixing then it might have been worthwhile, now we know that this is not the case best to turn it up again.  Once you do can you remeasure the temps (flow to/from radiators).  Explanation now much better, high deltaT across rads a concern but lets see what reinstating the pump speed does.

 

 

Been 2hrs since DHW has been used , only a small amount used and sitting at 47.06 c , should be 50c set for programme , I have been in 20mns and DHW  47,3  , no efficiency there , no taps used?

Once The water heating is off , I will get CH flows.

So checked again on Samsunf controller The water temp is set for 52c but never reaches that . Zone valve now switched off DHW back to heating and water at 48,6 Flow on controller at circ 41.5c 

Flow to and from Rads now at 33.7 and Return 26.3c

Posted by: @alfapat

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Flow to and from Rads now at 33.7 and Return 26.3c

OK thats a bit more reasonable albeit higher than might be expected, and gives some hope, but by no means certainty, that bypassing the buffer and secondary pump might work.

I think its now down to you to decide whether to try it or not.  If you do decide to try it be prepared also to swap out the 22mm for 28 and also be prepared to reverse out the bypasses (if you fit shut off valves its just a case of shutting/opening the shut off valves, which is why I suggested them).  Perhaps something to leave until its warmer, but not so warm you cant test it!  The key test will be flow rate which your controller should tell you.

Posted by: @alfapat

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Been 2hrs since DHW has been used , only a small amount used and sitting at 47.06 c , should be 50c set for programme , I have been in 20mns and DHW  47,3  , no efficiency there , no taps used?

the difference between 47 and 50 is small, perhaps the tank cant reach 50 on the heat pump alone.  Many only heat DHW to 48.  Unless its actually causing a problem I suggest to focus on one thing at a time.

Ok James , thank you for your thoughts there . The option to bypass being the the drawing that you sketched ? 
perfectly willing to change 22 to 28 mm , doesn’t make sense as it is .

Big question is finding someone with your knowledge up here .

please can you set out the resolve I need to apply to a Heating engineer in that I can explain a work around to sorting this . 

Posted by: @alfapat

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Ok James , thank you for your thoughts there . The option to bypass being the the drawing that you sketched ? 
perfectly willing to change 22 to 28 mm , doesn’t make sense as it is .

Big question is finding someone with your knowledge up here .

please can you set out the resolve I need to apply to a Heating engineer in that I can explain a work around to sorting this . 

Yes the bypass is as I sketched, although I should sound the note of caution that, as I don't have a full system diagram, there may be something else that needs to be taken into account.  

Its a very simple plumbing job that needs absolutely no knowledge of heat pumps whatsoever.  I try just explaining to a local plumber that you have been advised to rig up a switchable bypass to the buffer tank and secondary pump, so you can test which works best, and all you are asking him (or her) to do is the plumbing.  With a bit of luck someone will say yes.  If you cant persuade anyone to do it then your only option is DiY.  As I say upthread the key thing to check once its done is the flow rate seen by your heat pump which should be somewhere in the UI, probably under info.  If it isn't then the key thing to check is that the heat pump doesn't 'complain' about low flow rate.

With a bit of luck flow rate will be fine and you can turn down the WC by about 5C.  If it isn't you have lost the cost of the plumbing work.  I cant honestly see a way to be sure without trying it.

@jamespa Thanks , once again! 
Is that not the flow rate shown on that page I posted, 16L/pm or is that a completely different thing you’re talking about, and what is the WC please. Weather compensation?