Jan 2023  980kW, Jan 2024 1006kW and Jan 2025 903kW

My first winter with a heat pump too.

3 bed bungalow - 90 sqm (ish) plus cellar, average but patchy insulation, built into a hill & a bit exposed, in the SW.

6kw Daikin monobloc run on pure weather compensation, heating 180ltr tank 50º every other day atm. 

Jan '25  504 kwh 

Replying to the OP:

Jan 2024 = 1034 kWh

Jan 2025 = 1185 kWh

which is around the 15% more I'd expect given the colder weather.

I have a dormer bungalow too, and the upstairs insulation is the issue - through the 'walls' leaking into the eaves, and the doors leading to the eaves storage. It's harder to get to and insulate the 'upstairs' for obvious reasons. Grab a thermal camera and see if you have any cold spots that need sorting out.

Here is a video on how to adjust your curve, it’s the same process I showed you to access the curve just hold down the menu button to access the adjustment menu 

https://youtu.be/-983aLzVZ_I?si=Hxs3yAoH_mSb52ag

You're already using WC but I'd take a small bet your savings will be 10 to 15%... or more. By lower temp curve, more efficient usage...and maxing the tariff

I think I can use batteries to avoid the peak cost … but yes I will watch that

Ok thanks I think I am getting there (slowly) last question- how do I adjust the WC to balance the house when everything is open? And should I remove all the timed constraints on water and house heating (from the Mitsubishi controller)

You adjust the end points of the sloped line.you presented earlier.  This will be somewhere in the menu, probably the installer menu.  I would reduce the flow temperature at the low end (oat -10 I think) a degree or max two degrees at a time, perhaps no more frequently than once every 12 hours.  Once it gets close less frequently.  You should probably set times controls to avoid the expensive cosy period only.

It may take several days to get right.  Please do read a bit about it before leaping in though, particularly in the manual.  Don't expect instant results.

Also turn off auto adapt whilst you go through this process.  Probably you won't turn it back on.

PS. If you do initially massively overheat your house that's great news.  It means that you will make larger savings when you get the WC curve down.  

upd… all thermostats off, all trvs fully open. Feels like I am taking an enormous gamble to efficiently overheat the house - but I’m trusting you guys !

upd2… and WC dropped to 32degree flow at -3 and 25 degree flow at +15. Let’s see how we go!

Is this the temperatures? It is cold today!

Yes thanks, good plot

if I turn up all the trvs and turn off (up) all the thermostats to force the whole system to be completely on all the time won’t the house just get very hot? Sorry for the stupid question but how will the temperature be controlled with no controller operating?

Yes initially, but then you turn down the weather compensation curve until the house is at just the right temperature, thats the whole point.  The weather compensation system then adjusts the output of the heat pump according to the outdoor temperature so as just to balance the loss from your house (which is determined by outdoor temperature principally).  It is a bit counterintuitive initially, but it works, actually rather well.  As importantly doing it this way means that your heat pump is operating at the lowest possible flow temperature which is the greatest efficiency.

I suggest you spend a couple of days reading about weather compensation on this site and possibly also heat geek before tinkering, so you understand it.  Its not new, in fact its been compulsory for boilers in some european countries for a couple of decades because it makes boilers more efficient too.  In the UK we ignored it and it has cost most of us an extra 10% on our heating bills.  With heat pumps the effect is greater so we can no longer ignore it.

My house (and that of many others on this forum) is running on pure weather compensation with almost all radiators open loop, no TRV, no thermostats.  It works brilliantly.