@jamespa thank you, I'll start recording these, I can see them on the Onecta App. In the heat loss document it gives LWT range 35-50C, minimum ambient temperature -8.4C, I don't see anything more detailed than that, not sure if I should? I have a 180litre preplumbed Daikin cylinder which I think includes a buffer.

Are you able to post a photo of that 180-litre cylinder please @mairia ?

We can soon work out what it's meant to be doing once we see how the pipework is arranged around it.

Thanks

@transparent apologies I missed your post. This is a photo of the cylinder.

Thank you to everyone who has commented on this. I decided to initially send a Subject Access Request to the installer to see whether having sight of their records will help me decide how accurate the information given by them has been - though they have at least a month to respond to this. Today I sent a 'Something's Gone Wrong' report to MCS and will see what response that brings. I've also notified the installer that I haven't been reassured by their replies and will be contacting MCS in the first instance. The recent podcast from the Renewable Heating Hub on heat loss calculations was extremely helpful too. I'll report back on any developments.

@mairia thanks for the update. I was going to follow up with you. Please ask MCS for a copy of your heat loss survey/report. If they don't have one on file for you, I will take this up on your behalf with MCS.

@editor thank you, I've checked and did include that question. I'll keep you posted 🙂

Posted by: @mairia

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@transparent apologies I missed your post. This is a photo of the cylinder.

The literature online does indeed suggest a 20l buffer tank 'which can also be used for hydraulic separation'.  This suggests that Daikin are not saying it must be used for hydraulic separation, it would help to know if yours is which comes back to determining how it is connected.

I cant quite tell how the plumbing is connected and thus cant decide whether or not there is a buffer tank.  Is there a water pump in the vicinity?  Do you know which of the pipes shown are the feed/ return to the heat pump and where are the emitters connected in this picture.  Perhaps @transparent can see something I cant! 

How is the  monitoring going, is anything becoming clearer?

@jamespa I don't see anything that would help me know what pipework goes where. I don't see a water pump anywhere, and actually have a vague memory that the installer may have said the buffer tank wouldn't be used for hydraulic separation, but I'm not certain. Monitoring on the Onecta looks overall ok to me with LWT being what I would expect for outside temperature looking at the heat curve. Although sometimes LWT is maybe 1 or 2 degrees lower than I would expect. I don't know if there's any way to check if the DHW is heating at those times, would the LWT reflect that? I did get one reading of outside temperature 10 and LWT 49! I didn't know what to make of that. I'll try to be a bit more organised at monitoring as I've just been checking it randomly.

Posted by: @mairia

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@editor thank you, I've checked and did include that question. I'll keep you posted 🙂

Perfect. Once you've received everything, can you please email me the lot so I can review the documentation provided and whether anything else was missed.

@editor will do 👍

Thanks for the additional info

Posted by: @mairia

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Although sometimes LWT is maybe 1 or 2 degrees lower than I would expect. I don't know if there's any way to check if the DHW is heating at those times, would the LWT reflect that?

I wouldnt worry about a couple of degrees.  If DHW is heating you would expect LWT to be higher than normal which might explain

Posted by: @mairia

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I did get one reading of outside temperature 10 and LWT 49! 

Posted by: @mairia

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I don't see a water pump anywhere, and actually have a vague memory that the installer may have said the buffer tank wouldn't be used for hydraulic separation, but I'm not certain.

If there is no water pump visible either there is no buffer or its actually plumbed as a 2 port volumiser.  This would be good news.  Please let us know if you find one!

As I recall your problems were:

• Lower SCOP than expected (2.7)
• House a bit underheated in coldest weather.

I think you also said you were setting back at night and I suggested

1. that cancelling the setback may fix the cold weather problem (you may have to turn the WC curve down a bit, which would likely improve SCOP)
2. that if (1) doesn't fix it, turning up the WC curve will ferret out whether the heat pump is undersized or not
3. that monitoring IAT, OAT and LWT will help narrow both problems and, if necessary, provide evidence to the installer/diagnostics on what to do next

Is that a fair summary of where this is currently at?  Its always in my mind keeping a focus on this otherwise its too easy for the discussion to go off at a tangent. 

Actually I've double checked my current heat curve settings and the LWT seems pretty much correct for the outside temperatures.