Assuming a high thermal mass UFH system (50mm screed), is there any point in getting quotes from Daikin only installers, or are Diakin always problematic with such systems?
I have see lots of threads with people having issues with unpredictable flow temperature from Diakin when asking for low flow temperatures. Is anyone not getting these problem, eg a Diakin working well with UFH using default settings?
Mine is milled in UFH so not a huge layer on top, but a fair chunk of concrete below.
Daikin min output temp from compressor is 25C, any lower and it uses backup heater afaik.
Tbh I think the key issue at 30C or below is that the emitter output just drops significantly which is below the minimum output of the unit, rather than the unit specifically struggles at that temperature. Hard to compare without moving from one unit to another manufacturer on the same physical install 
I guess you could expect better SPF from the average flow temps than what the daikins generally achieve:
The only reason I am considering a Daikin is Octopus low overhead install and their very reasonable maintenance contract.
I don’t believe Cosy Heatpump will be optimised for UFH as it is not Octopus target with them.
Shame there is not a degree-minutute software update for Diakin or a Octopus like installer for Vaillant. (I happy to pay difference in trade price of unit.)
I am thinking a 4 port buffer with UFH mixer could improve COP of a Diakin with high thermalmass UFH given the low COP people with very low flow temperatures are getting compared to people with normal flow temperatures!
tbh i dont think any octopus installs on here are running anywhere near the design temps , if you look at them most are less than 35 degrees when its below 0
I keep thinking COP of 3 with 30kwh of batteries will give lower running costs then COP of 4.5…
Oh if you are being pragmatic then you can definitely get a cheap install and still achieve reasonable running costs with the Octopus approach. You just have to get over looking at the Vaillants performance 
The issues I am getting is even the basic “leaf cleaning” service needed for the Vaillant warranty is at least double what I pay for a boiler service and gassafe paperwork. So with Octopus it is not just the cheaper install, but much cheaper service etc.
I also don’t like Vaillant not surporting RS432 control systems like Homely, so no automatic way to optimise for different electricity tarrifs.
