Sounds perfect 🤩 

@boycey, welcome to the forums. It sounds like you’ve set everything up really well. Are the rooms feeling warm and cosy? If so, take a look at your SCOP to ensure you’re achieving this efficiently. Anything over 3 is a good indicator that you’re on track for efficient operation. Keep us updated.

I have a Samsung unit in a new build house and it seems to use more energy if I run it really low and slow. When it first went in, only about a month ago, I had the weather compensation was set so the water leaving temperature was around 25° most of the time with an indoor temperature of 20-21° 

Setting the weather compensation so the WLT is about 30-35° is more efficient for my system at the moment, but the temperature indoors isn't as consistent as the heating isn't on much, especially at the moment with it being warm for December.

@editor Hi Mars, on the ecodan FTC6 it shows consumed for Dec 148kwh delivered 388 kwh. So is that a COP or SCOP? Of 2.65? So not very good? How could I improve this. I think my delta T is low, (if that's the difference in flow temp and return) it's about 3. Only been with this system since Oct so lots of learning

@johnnyb Perhaps adjustments to the WC curve so as to raise the LWT to approx 30 degrees might be worth a try? It is a cat and mouse game of course due to all the variables but it sounds as though your original 25 degrees was just a little too low and the 35 too high? Regards, Toodles.

@toodles hi, I think you may of mis understood my post, I'm happy with my temps atm, and I'm monitoring them as the oat getting nearer 0C and will tweak as needed. My post was, am I thinking right, aiming to keep the third party stats above the obtainable room temp so they are always calling for heat, ie so the loops are all open and flow temp is just right to keep rooms at, for example 20.5c or whatever the comfortable level is for any one using this thought process. If one can get the weather comp curve just right, the ufh will continually run just the right flow temp, ie low and slow.. is this the right way to try and run my heat pump.

Posted by: @boycey

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.. is this the right way to try and run my heat pump.

Basically yes!

@boycey The only added wrinkle for your flat is that 5kW is a lot for a 2bed flat so your pump perhaps could be on for less time. UFH often has a “long time constant” so it will stay warm for a while after the heating switches off. Low and slow is certainly ideal, but you might be able to drop your overnight set back to less for example. 
What electric tariff are you one you might be able to use cheaper periods only as a further example?

Are you a newer build or a refurbished older building?

@judith ĥi, I managed to get on to Ovos limited trial for their heat pump tarrif, 15p  a unit for all heat pump consumption. It's a new build apartment.

@toodles I have been trying different temperatures and trying to get a balance between comfort and efficiency, but haven't got there yet!

I commented as I have a similar situation, small heat pump in a new build with UFH, and I can run the flow temperatures very low because the heat loss is very low, but it seems that not all heat pumps are as efficient at really low temperatures so it may be worth experimenting with higher temperatures to see what works best. Most people seem to require a lot higher flow temperature to keep the house warm but if the floor holds the temperature for a long time and releases it slowly having the heating on for less hours per day, but still maintain a constant temperature, might work out more cost effective. It seems to be helping my electricity consumption, but it has also been a bit warmer and less windy the last week or two.

@johnnyb Where is the ‘envious’ emoticon? Toodles.