Hi @john-castle , I’m new here too. I also have a Daikin. It’s the altherma 3 8kw. My system is a little different from yours because I have a mixergy tank rather than the Daikin, because of low water pressure. When originally set up I had a buffer tank and to go with that a second pump, which you may have too. This caused all sorts of conflicts and there has been a reconfiguration removing the second pump and converting the buffer to a volumiser. The quiet is now deafening, as they say. That second pump was a noisy beast. I have noticed a marginal uptick in cop.

There are lots of briefing papers on this site about various things,and the heat geek site can be very helpful too. It appears that unless you have a very large property or maybe an unusual configuration buffers are no longer considered helpful and to the contrary are a burden on the system and reduce efficiency. I should add as a bye the way, the second pump would not have had its power consumption measured by the heat pump, so whatever reduction in power I had from that being removed is also a bonus.

like you I just have one zone and Trv’s are set to max, hopefully meaning they aren’t interfering with anything.

what size pump do you have? And what is your heatloss calc and associated temp range?

@john-castle, I’m surprised that with that level of refrigerant loss, you weren’t seeing any error codes on your control panel. Refrigerant loss often manifests as unusual or erratic errors.

Mars, so was the Daikin engineer but no errors came up on the MMI ! My understanding is there isn’t a pressure gauge on these units so unless you see a leak ( rusty oil like substance ) you wouldn’t know the state of your refrigerant! Slightly worrying as he seemed to think it came out of the factory like this. I asked the question about checking the refrigerant when serviced and my understanding from what he said the only way was to weigh it. Having said that I am deaf and rely on a cochlear implant for hearing and don’t always catch everything correctly!

@john-castle thanks for the explanation. My only reason for asking is because defrost errors (in the absence of defrosting) can be an indicator that there's been a loss of refrigerant which is what I covered to some degree here:

In our case, we didn't have a refrigerant leak, it was the sensor, but it could have been the refrigerant. 

@terry1812 unfortunately I have the 9kw pump ( if only I new what I know now ) I know a 8kw pump would work more efficiently for my house. It’s been running for a little over a year now with only a third of the refrigerant and not once has the house felt cold! We have a wood burning stove in the lounge which we like to use on cold winter nights , none of the installers take this into account ( I assume regulations say you can’t) so consequently I have a pump that’s over sized and can’t modulate down below 900w consumption! I had three surveys and they all came in about 8-8.5kw. 
The buffer tank on the pre plumbed Daikin unit is quite easily turned into a volumiser and only appears to be about 30ltrs and appears very little separation of outlets, basically if the leaving water temperature of pump is 40c the pump flow pipe is 39.5, flow to radiators is 35c return from rads is 30c , return to pump 35c. So basically the heat pump at 40c heats the buffer to 35c. I’ve only got one zone, loads of big radiators design temp 45c @ -3 can’t understand why I shouldn’t be sending the heat straight from the pump to the radiators and so not having the pump having to work so hard.

@editor interesting, so I think now the pump frosts up differently, it appears to be a finer frost on it. So the first time since we had the pump ( just over a year ) my wife comes running up to me in the office panicking saying the pump is still broken I think it’s on fire it’s smoking and feels hot! Might be a coincidence but this never happened before the refrigerant was changed. The pump would have a thicker ice on it would drip more but not steam!

@john-castle Yes that does sound problematic, I very rarely touch 900w and if I do I am wondering what the problem is? Who did your install. There is a guy who had an octopus install and they swapped out his 9kw for the 8kw. If your installers aren’t helpful you could talk to Daikin, they may be able to help you reconfigure. Did you get the grant? One of the issues with the grant can be that if your heat loss comes out as yours did, you have to put a pump in at least equal to the heatloss. Which when you are borderline like you are is tough. Tough because amongst other things there are factors that Don’t get taken into account with the heat loss. So for example if you have heat retaining curtains, and use them, the heatloss avoided can be quite significant. However they can’t take it into account because they are part of the fabric of the house.( Pun intended). So the next occupants may not have them…etc etc. The other reason it’s problematic is because esp with the jump from the 8kw model to the 9kw, is that practically you only need that little extra for the bottom end of the temp zone, which is a very short period. Also because they have to quote 21c ( either for total house or certain parts depending on age of property) for MCs rules and to get the grant. 

Could be worth a conversation with the installer or Daikin, and with Daikin I think you do have cause for complaint/ leverage because of the refrigerant issue. Also did they give you details of the heatloss calc, have you verified it?

@terry1812 it was one of bigger installers, not octopus or BG. The cost was very competitive, may be I should have paid more and gone with a valiant 7kw which one company quoted. However the price difference would have taken 10 years plus to recuperate. I’m finding if I’m not careful I’m getting obsessed with the pump efficiency which in fact if I got it closer to a cop of 4 ( at the moment it’s 3.5 ) would financially make a difference of less than £100. I’m fairly confident changing the buffer into a volumiser during the summer will make a 10-15% increase in efficiency. I have to partly drain the system down as the installers put the inline filter in the wrong way round anyway. Probably do it myself really finding it all to much effort and agro to get trades to sort out sadly. I’ve done quite a bit of plumbing in the past so fairly confident! I want bother to try and get it changed as once it’s reached the desired temperature it just switches off for a hour or so till temp drops again and isn’t using much more electricity than an 8kw unit. Will probably report back next year on what difference the change made!

@john-castle Yes, I too have become somewhat obsessed, trying to comprehend what should in essence be something simple. As  soon  as external temps reach 15-16c , hopefully by mid April I’ll turn the heating off and put it back on again end Sept early Oct.  just let it deal with the occasional demand for DHW.