Thanks again John,
Maybe this is something I have to live with fttb.
As long as it isn’t damaging anything then it’s not the end of the world.
My heat pump performs pretty efficiently and is heating our house and water.
It’s a fault but maybe not serious enough to be a performance or warranty issue.
It’s a bit like pulling away in 2nd gear… hard to know how bad it is. We should scour hpm for others doing this. Liquid in the compressor must reduce lubrication… Not ideal
I don’t like the idea of it much I must admit.
And it is not working as it should, or maybe not as well as it could.
But getting anybody to act on what they see as a non or insignificant issue is not easy.
Actually, @johncantor, I understand that liquid is very deliberately injected into some heat pump compressors (see https://core.ac.uk/download/4957385.pdf).
Based on my reading of the operating manual, my Samsung scroll compressor rotor requires oil injection for lubrication and for sealing machine clearances. This is achieved with a polyolefin-based refrigerant-miscible low temperature oil that - as I understand it - passes through the compressor with the refrigerant, and is separated on the discharge (by gravity) for recirculation to the suction.
So some liquid refrigerant entering the compressor may - within limits - be tolerable.
Any thoughts?
Sarah
Yes, @johncantor that’s what I have observed 
.
I’m still gathering data using borrowed @glyn.hudson’s monitoring gear (awaiting colder ambient conditions to verify), but I’m close to concluding that (on my Samsung at least) your 20degC margin is almost a “rule”, which will simplify the Outdoor Unit thermodynamics analysis…
Sarah
Daikin don’t want the public to have this information because it exposes how mediocre the product is.
I would be suspecting a software driven refrigerant side issue for your DHW performance. Wrong compressor speed, expansion valve position, and fan speed for the operating conditions that is having a detrimental effect on heat output for a given electrical input.
This would be night and day visible if you had access to the internal data. And probably readily fixable unless the reason it happens is that the designers of the unit cheaped out on sensors (omitted some) and the consequence is that it occasionally “finds a local maximum” instead of finding “the global maximum” optimal operating point.
Else perhaps there’s a sticking/bypassing reversing valve or a sticking/bypassing pressure relief valve inside the compressor that knocks back the cycle efficiency?
Either way it’s a “raise as formal evidence of a defective unit with octopus” job; such that it’s on record as having failed within the warranty period. This avoids any strategy of the vendor “running down the clock” and hoping that your warranty times out before they’re forced to act.
Perhaps wait for it to get bad enough to justify the hassle of replacing it if not that fussed; or if more concerned raise with MCS as evidence that the installation is not to the highest standard if the equipment has intermittent operating faults and you’re not getting straight answers from Daikin?
Hi Marko,
Yes, I am pursuing it with Octopus as they supplied it and it is their responsibility to put it right.
I think the internal data is accessible using ESPAltherma or p1p2 (?) but I don’t see that as something an end user should need to do to prove a fault.
My warranty is for seven years so I have a while to deal with it.
Something has changed recently. It had a firmware update in May 2024 but I haven’t noticed any issues before 14 September 2024, that is not to say that isn’t when it started though as the weather is different now.
I don’t know what to make of Daikin engineers that I have dealt with, they either play dumb on purpose or they just don’t know what they are talking about, I suspect the latter.
I don’t really know how mediocre their product is, it works well in my house in terms of efficiency but I don’t know how different a heat pump from another manufacturer would be. I also have know way of quantifying the quality of the components used in their heat pumps, how bad or good they are compared to others, I really don’t know.
With a Daikin service engineer is it a hydronic expert or an aircon/heatpump expert?
To be fair I wouldn’t expect their first line of support to know more than to follow the basic diagnostics/troubleshooting provided in a guide and second line of support at least to start diagnosing more complex issues like this.
As for Daikin updates, I’ve documented several obvious errors in my MMI where settings don’t align (my 60% pump speed during sampling actually sets it to 90% etc) but the UK rep doesn’t hold out any hope for an update for those. Then there’s the power limitation not working for the smart grid controls too.
@SarahH the daikins do a mandatory oil recharge reverse cycle every 12 hours of compressor runtime (non continuous), which can cause a lot of confusion for “defrosts” during warm weather, or shortly after starting up. 
Hi Ben,
The first line of support does need to be able to recognise a problem in order to get to the the next stage.
The first line of support has dismissed my reported fault as normal operation.
He says that as the flow temperature is rising there is nothing wrong with the heat pump. My heat meter is not 100% accurate (true). He didn’t understand what the heat generated part of the graph meant and concluded that part was inaccurate whilst the rest of the data was accurate. So, he accepted that the flow temperature, the return temperature and the flow rate were accurate but claimed that the heat produced shown by the graph was inaccurate!
He actually said that the heat produced by the graph couldn’t be correct as it made no sense - DOH!
I don’t think you need to be much of an expert in either field to see that something is amiss when shown graphs of normal and abnormal operation.
I haven’t heard anybody yet say that something doesn’t look right other than the Daikin engineer.
You can use the Daikin API for Diag + Home Assistant via - GitHub - jwillemsen/daikin_onecta: Home Assistant Integration for devices supported by the Daikin Onecta App
No need to take the cover off the Monoblock!
and to compare the ESPAltherma
I could if I had any idea what that means!
I have been looking back through my data to see if anything has changed.
Up until 25 June 2024 the flow rate on DHW was around 19lpm and the dT was around 5c
From 26 June 2024 the flow rate for DHW has increased to over 24lpm.
This is why I am not seeing the dT I used to.
As @johncantor suggested, maybe this flow rate is too much for the combination of my cylinder and heat pump?
The problem has actually been going on longer than I realised.
The DHW performance starts to deteriorate noticeably as the weather cools after the summer.
I think the problem is my tank doesn’t like the increased flow rate?
This interests me @meatballs. What compressor type is used in Daikin’s? I had assumed that most lower cost heat pumps were moving towards scroll type.
What is actually recharging here? The oil reservoir? Do you have any diagrams from your manuals? And do you know how your compressor keeps itself lubricated if not continuously oiled?
Many thanks,
Sarah
If your tank is having issues with the higher flow rate go into the installer settings and check what tank you have set It is in installer options → domestic hot water.
Page 193 of the installer reference guide has some more details on this and the options available.
Just an idea for something to try
I just had a thought, my heat pump was serviced in the summer.
Guess what date - 26 June 2024, the day my DHW went wrong.
Perhaps the unit is unable to manage expansion valve position properly / reliably if the water side DeltaT is too small?
Service heat pump= clean strainer (or fiddle with settings) = higher flow rate and lower dT?
Thanks Marko.
I don’t know what is actually causing the problem with the increased flow rate, but the puzzle has come together. I can see when the problem started and what changed to cause it.
Your suggestion seems entirely plausible based on my limited technical knowledge.
What is surprising is that nobody at Octopus or Daikin recognised the symptoms and the Daikin engineer wasn’t even prepared to investigate as he had already decided that the heat pump was working properly and the only issue was an overly fussy home owner.
The number of people at Octopus with a level of heat pump understanding beyond “see pipe join pipe” is relatively small. They exist; but there are not enough of them to serve the installation base that they have built up. Their managers are not concerned by this. The situation will continue.
Same bunch are in the papers again this morning for false advertising and breaching the honesty clause of their supply license by claiming that they’re obliged to replace dumb meets by regulations. Whoops. Hired too many corporate bullies from their competitors it seems.
my strainer was cleaned during the service and i noted a flowrate increase on the DHW.
I remember that the filter was clean as I was outside with him when he was checking.
But, in any case, the filter was clean when it was installed (I would think at least) so any filter cleaning should only have returned it to its previous state.
I do recall him checking stuff on the MMI and I remember a conversation a bout stuff but not really the details.
I don’t really know what the cause is, I just need to turn it down somehow.
