@kev-m Thanks for the reply. 

Picking up on your first observation, what should the flow temp be set at for UFH? On the issue when the outside temp drops the ASHP still works, running for days on end trying to achieve flow temps but doesn't get to above 25deg.  

I agree about the installer returning to rectify but there goes the problem.  It has been like this for a year now and they have had numerous engineers back, 8 and counting but no diagnosis.  I  have no confidence in them as they tell me its all fine but once the ambient temp drops the issue comes back. We are desperate for answers and rectification and have also tried independent installers but none seem to be able to diagnose and offer the same advice to go back to the installer which is where it all falls down.  There seems to be a lack of knowledgeable engineers out there, or my area at least who can help.

@Leftbacks, it's hard to say but most ufh systems seem to work around 35-40 degrees.  Maybe others with ufh can comment. My house was built in 1990 and has radiators and the flow temp never goes above 43 and this keeps the house warm. 

When  you say it doesn't get above 25 deg, where is this measured? Is this the flow temp in the ufh system or the flow temp as the water leaves the ASHP?  I assume your HW is OK; if so the ASHP is capable of heating.  It's possible the thermistors reading the flows are faulty but you really need them checked.

Have you tried calling Mitsubishi directly? They have a customer support line and I have found them helpful.  I can't remember the number but here is a link. 

https://les.mitsubishielectric.co.uk/contact-us    

@harriup 

hi. I was interested to read your post regarding freeze stat. My system is set with it on but is also glycol loaded. How do i turn it off. The company that fitte my pump went bust shortly after finishing the job.

cheers,Stu

@stub13 

You'll have to go into the service menu which is the spanner option to the right on the second of the main screens. Just Ok the password (assuming it is the default) then scroll down to Operation Settings, you'll then be asked to shut down the service - ok that, then scroll down to Freeze Stat Function. When selected the screen has two halves, the circulation temp on the left and the ambient temperature on the right. If you decrease that number it drops from 3 to ** - this symbol means the freeze stat function is deactivated. I can't remember whether you need to ok that after the change, but otherwise just return back out of the menus.

@harriup 

thanks for taking the time to answer my query. I have now turned off the freeze stat which, I believe, is how it should have been all along. 
cheers. 

@kev-m

I think that you have been running your system in Auto Adaptation mode for some time now, so I would be interested in how it is performing.

How close does it keep the actual IAT to the desired value?

How does it respond when your heat pump cycles?

@leftbacks

Did you manage to resolve the problems with your system?

@derek-m Still unknown at this stage due to number of factors but early indication is that its still the same.  Since the last post we had to get an expert survey for legal reasons which a found a buffer tank was needed and pumps changed so the contractor has carried out this work.  Also the ASHP was changed by Mitsubishi due the compressor being faulty, not sure if this was due to it having to work excessively but its only 18monhs old.  Our hot water has been fine no issues there with flow temps etc.  We ran the heating for the first time on Monday when the outside temp was around 8deg (where we had the issues previously) and it took best part of 24hrs to get the rooms to around 20deg.  I don't know if this is normal for when first operating after not being in use or if this is what we can expect as it gets colder outside. Typically the outside temperature has since risen to double figures so its achieving the desired room temps. 

Posted by: @leftbacks

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@derek-m Still unknown at this stage due to number of factors but early indication is that its still the same.  Since the last post we had to get an expert survey for legal reasons which a found a buffer tank was needed and pumps changed so the contractor has carried out this work.  Also the ASHP was changed by Mitsubishi due the compressor being faulty, not sure if this was due to it having to work excessively but its only 18monhs old.  Our hot water has been fine no issues there with flow temps etc.  We ran the heating for the first time on Monday when the outside temp was around 8deg (where we had the issues previously) and it took best part of 24hrs to get the rooms to around 20deg.  I don't know if this is normal for when first operating after not being in use or if this is what we can expect as it gets colder outside. Typically the outside temperature has since risen to double figures so its achieving the desired room temps. 

 

Since numerous people have tried to resolve the issues with your system and appear to have failed, I suggest that we go through your system step by step in a logical and systematic manner.

Might I ask how technical are you, so that I can assess what level of testing I could suggest. Do you have a suitable thermometer with which to measure the temperature of pipes etc?

It is probably best to start with what we know.

You have no problem with producing DHW, so that would indicate that the heat pump works and is capable of producing a high Leaving Water Temperature (LWT).

It would appear that this warmed water is not getting to your UFH loops.

Can you produce a schematic diagram of the layout of your system, how it is piped and what equipment (pumps, valves, buffer tanks etc.) has been installed. Please provide photo's and/or details so that the individual devices can be identified and their specification checked.

@derek-m I would say that I am okay technically and learning all the time through this process, Also I have digital laser thermometer that I can use to check pipe temp.

 I have attached some photos of the set up and a handrawn schematic with the pumps etc marked

@leftbacks

Thank you for providing the detailed schematic and photo's. The only comment that I would make is that I think the ESBE valve is a 3-port device, direct the flow from the heat pump to either the hot water cylinder or the central heating system.

Your system is quite complex with 4 water pumps, which I suspect may be part of the problem.

As a start, could you measure the temperatures at the pipework around your system and add these values to the schematic diagram. Pay particular attention on the inlet and outlet pipework of the buffer tank.

Has your system always had a buffer tank or has one only been installed recently?

@derek-m Thanks for the feedback, the buffer tank was recently fitted in place of a low/loss header tank (think that's the correct terminology).  I will record the pipe temperatures and come back to you.