I have sketched out my thought process to try and explain things easier. The hot water cylinder has a pre plumbed plate heat exchanger that I have tried to show. 

The idea I think could work however I am not sure if one pump is powerful enough? 

I also forgot to include the top setup has a bypass on both the upstairs and downstairs.

Thanks

I suppose the starting point would be to check the heat loss calculation for your home against the required Leaving Water Temperature (LWT) needed to meet this heat demand.

Since you have full UFH throughout your home I cannot, in principle, see any reason why you cannot remove the UFH mixing pumps and re-pipe the system as you propose.

You would probably need to check the specification of the main water pump to ensure that it can provide the required flowrate, with the head and size of pipework within your system.

You could probably keep the thermostats, but set them above desired room temperature to act as an over-temperature restriction.

You may also be able to keep the bypass valves provided that they do not bypass unless necessary.

Thanks for the reply 

unfortunately all my knowledge has come along after install so I never asked or saw any heat loss calculations  🙄

the best I have is the MCS certificate that states 45c flow temperatures and 3.79 scop (I wish) 

annual space heating 20,700 and water at 3,596

the EPC that was preformed after was 9,644 KWh heating and 2,954KWh water

with the weather outside colder now 0c the hes pump is reporting Lwt of 33c and the house is sat at 21c

The stats are currently set at 23 as temperature limiters that don’t ever get reached, 

I’m not sure how I could guess the amount of pipework? again I did not ask enough questions at the time and relied on them being knowledgable so didn’t see the underfloor plan 

Posted by: @rich

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Thanks for the reply 

unfortunately all my knowledge has come along after install so I never asked or saw any heat loss calculations  🙄

 

the best I have is the MCS certificate that states 45c flow temperatures and 3.79 scop (I wish) 

annual space heating 20,700 and water at 3,596

the EPC that was preformed after was 9,644 KWh heating and 2,954KWh water

with the weather outside colder now 0c the hes pump is reporting Lwt of 33c and the house is sat at 21c

The stats are currently set at 23 as temperature limiters that don’t ever get reached, 

I’m not sure how I could guess the amount of pipework? again I did not ask enough questions at the time and relied on them being knowledgable so didn’t see the underfloor plan 

If my understanding is correct, all this information should have been provided in a handover pack along with adequate training. If you did not receive a pack then I would suggest that you contact your installer and request one.

Thanks I did not receive a pack so will contact again, I don’t have very high hopes as the company who did all the plumbing had a MCS certified person “inspect” and commission the system. I was with him during the commissioning as got a 2 minute lesson on the controller and told if you have problems he could come back and do advanced things like alter the weather compensation curve. 
I have tried to contact the company last year I think and the response I got was that the MCS certified person had become extremely hard to reach even for them and was not really responding, 

unfortunately it has been a lesson learned in doing more research before starting.

This is why I want to fix the system myself if possible unfortunately the whole thing has left me with little trust of the next person coming and fixing it correctly 

@rich

No problem if you don't have all the details, but someone should have carried out heat loss calculations to be able to adequately design the system.

The fact that your system is operating with a LWT of 33C at an Outside Air Temperature (OAT) of 0C, would seem to indicate that you don't have any serious problems. What is your concern?

Yeah I hope some calculations were done I think the company just sent all the plans to Mitsubishi and they suggested this if I’m completely honest. 

The system seems to do well when it’s cold outside and struggle more with warmer conditions, 

my concern is due to the system running 24/7 in weather compensation the 5 pumps run constantly. I tried turning the temperature down so the heatpump turned off and measured the power before stopping the pumps and powering down and this difference was 300w or 7.2kwh per day I know it will take energy to move the water around the system but 1,500kwh in 6 months heating seems a lot ?

Posted by: @rich

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Yeah I hope some calculations were done I think the company just sent all the plans to Mitsubishi and they suggested this if I’m completely honest. 

The system seems to do well when it’s cold outside and struggle more with warmer conditions, 

my concern is due to the system running 24/7 in weather compensation the 5 pumps run constantly. I tried turning the temperature down so the heatpump turned off and measured the power before stopping the pumps and powering down and this difference was 300w or 7.2kwh per day I know it will take energy to move the water around the system but 1,500kwh in 6 months heating seems a lot ?

You are probably correct.

You should certainly be able to remove the mixing valves and UFH pumps, which would normally be required if you have a mix of UFH and radiators or a higher temperature boiler.

I would suggest that you ask your installer for details of the UFH pipework and capacity, since you may need to ensure the system has the minimum volume required by your heat pump.

As a test, you could try bypassing the Low Loss Header (LLH), remove the two circuit pumps after the LLH and put pipework in their place, then see if the main water pump is able to cope.

@rich seems to me like you should be able to do what you have drawn, yes the LLH is ruining your COP based on those temps you've measured. 

the fact you are UFH throughout is great, means the temperature down-mixing valves not needed. your pump electrical usage to move the water is indeed excessive. don't stress too much about not knowing the heat loss or head loss, you can take an empirical approach. If after re-piping so that its all done by one of your existing pumps, that one pump isn't quite enough (it'll be obvious, some areas won't get flow) its trivial to buy 1 larger pump. you'll still gain a lot on electrical usage. worst case you may have to tolerate some part of the house not being warm enough until you're able to get and fit a larger pump. although, looking at your pictures one of the pumps mounted on the cylinder looks "bigger" so you might be ok  - is that the one driving the primary from the heat pump outdoor unit?  what type pump is it?

Thanks for all the advice, I have contacted the original installer and asked if they can send over any information they might still have. 

You are correct the pump that circulates the heatpump is different its a UPM GEO 25-85 130 I couldn't find a great deal of information about it online but did manage to find this chart. 

I think as you have said my best approach is to do the modifications and monitor the results I remember reading you can check the flow using the FTC and I am fairly sure I could restrict the upstairs flow more to push it around other circuits as this always has a very low DT 

I cant seen to upload the screenshot at the moment but I found the chart here on page 38 

@rich a UPM 25-85 130 is fairly beefy, it may well be enough to run the whole thing. I run a 210m2 house on a single UPM 25-95 130.