you got the 9kW cosy as the smaller 6kW was not suitable for your properties heat loss

its not just the COP you look at, its the energy consumption in kWh per day.

My Cosy6 was running full operation the first winter as i hadn't completed the insulation in the new kitchen extension roof.

This winter period, the Cosy6 was much quieter, insulation makes a huge difference to heat loss. My rear extension is fully insulated, floors, ceiling, walls, to 150mm. It is always 2C warmer than the rest of the house

This Autumn, after the wall insulation is installed in the Lounge/Kitchen I will be rebalancing the UFH towards the Lounge

What would be very useful is if you could describe your system, in some detail: how you have it set up, how you run it, hub parameters etc.  

I do see the logic in oversizing these, I'm glad I have the 9.

Overall this is fantastic, sorry I haven't posted much, but I do feel like I need to post to say it's great, in order to give other people the confidence, especially if you are comming from an oversized boiler. 

In reality numbers/stats mean not as much as people think and decisions are made on if someone else has it working well, which is the case here 👍.

their calcs were 20% higher until I challenged them to redo them.

they got 2 radiators transposed as the survey numbered the bedrooms opposite to the way they were used.

i swapped 2 radiators and fixed their issue, easier than battling the press 1 for idiots or 2 for numpties

i turned every TRV to full open and ran the system full on and turned down the lock valves until the output of each radiator matched the heat loss of the room.

took around 2 months tweaking to get a balance

i run it with a master cosy pod in the lounge and a slave pod in the master bedroom

ive been improving the insulation for the past 6 months and have 1 final stretch of outside wall to add 50mm of rockwool to to make the lounge/kitchen cosy; it’s currently 1C under temp but i can cope with that as i don't have a fussy partner that cant put a sweater on :-

my cop has improved from 3.5 to 4.8, and the UFH is best thing to have paired with a heat pump

G

These are the figures for the year:

SPF (SCOP): 3.91

Input Power: 3.39 MWh

Output Power: 12.88MWh

I think the headline takeaway I have is that these figures are pretty good.  First season so it needed tuning in and this thread highlights some of the issues I've had.  The design as presented by Octopus was for a SCOP of 3.6 at a variety of room temps (supposed MCS required temps) with a heat loss of 8.5kW and a flow temp of 50c at -3.2c.  

Overall, I would say I'm mostly happy:

• we haven't been cold through the winter and have maintained temps at 22c or above (and early days, very above!) which suits my wife very well.
• Octopus service has been (mostly) good.  Sometimes a little slow to respond but they did engage with the overheating problem and with radiator replacement for two rooms that were incorrectly sized.
• Installation was great although they didn't allow the team enough time to do it in one visit.  Certainly no real problems and redecorating was minimal - really just painting copper pipes which they adjusted for larger radiators.  
• The price of £6.5k seemed reasonable for the installation given it involved taking out a radiator and changing 14.  Anyway, Heat Geek wanted me to stump up £18.5k for the same job! 

It's not perfect though:

• Although we maintained temperatures, I'm disappointed that Octopus install with a thermostat and have it running under the same approach as for a gas boiler.  So, one small area of the house is "at temp" whilst the rest of the house warm and cool based on that area's heat loss.  This specifically was a problem I wanted to do away with by installing an ASHP.  I don't truly understand their thinking behind this approach - they state running costs - and especially their argument that involves wording along the lines of "when the house reaches temperature the Cosy turns off": clearly "the house" doesn't reach temperature, one small area of it does.
• Control was very difficult.  With the thermostat in the living area, the rest of the house was either too cold or too warm.  I found that placing the thermostat in the downstairs toilet, the smallest room in the house with two outside walls and a small window, allowed for the "best" control.  However, control wouldn't be the best term: I could set the required temperature to be 19c, 20c, 21c (and I would guess any temp) and regardless, the rest of the house was maintained at 22c - 23c.  In other words, it would seem the rate of heat loss of the downstairs toilet is sufficiently high that regardless of the called for temperature the Cosy would operate enough that a nice stable temperature was maintained elsewhere in the house.  I have had to turn down 3 TRVs and put a decorators cap on another; most, if not all, of the radiators have their LSVs set to about half a turn.  The landing radiator never comes on because its always too warm in that space (it does work, we were reaching 26c with the TRV fully open.)
• It's extremely difficult to speak to someone technical to help work through problems, despite asking.  I'm pretty sure that I could tune this better with that sort of input.  It's needed because the amount of data we have access to as customers is extremely limited: OAT, Input Power and Output Power on an aggregated or averaged hour basis.
• The heat loss survey was redone and was calculated at 7.5kW, so -1kW over the original calculation.  A new radiator schedule was generated which gave a total heat output of +1kW over the original schedule.  So basically, my heat loss reduces but heat output increases, and the re-survey was undertaken because the house was overheating!  I queried whether anyone sanity checked this but got no answer.  I've sort of lost trust in them a bit to be honest, especially as the general feeling is that they are overly pessimistic with the heat loss calculation.  
• They won't share the data used behind the heat loss calculation so it's not possible to perform a sanity check based on gas usage say (I had no inclination to get to grips with heat loss software.)
• The whole ASHP experience is a science project for the home owner and it shouldn't be - this is an industry issue not an Octopus one though.  I spent around 3 months trying to get this system operating to a point where we weren't too hot before calling it a day for this year.  I feel sorry for homeowners who are less able to do this. 

The future:

Anyone who has followed this thread may remember that I was able to make an adjustment so the flow temperature is 50 at -10c, further pointing to an incorrect heat survey.  Subsequently, Octopus have changed their app to allow Cold Temp WC control to be set down to 46c at -10c and have added a quiet mode.  When next season rolls around I still want to get this running without thermostatic influence, purely on WC, something I couldn't do this season because I couldn't adjust the WC low enough until too far through.  I feel it should be possible given the ease at which the Cosy was able to raise IAT to 22c and it ought to make it even more comfortable and more efficient.

It says hush mode caps compressor and fan at 60% so to get 8.3kW heat out is quite the achievement.

With a Cosy, hush mode is a simple on/off option, with no scheduling possible.

Ah, not so useful then

Octopus will catch up sooner rather than later.

For sure, hopefully before next winter!  

On the Vaillant, programming NR mode (both on/off and hours of operation) is an installer level option.  I think this 'decision' varies from manufacturer to manufacturer.  I can understand the reluctance to make it a user option given the side-effect.  Fortunately the installer password in 00, pre-programmed into the interface. 

There is even the option (buried deeper in installer mode) to change the magnitude of the limit.  The range you can select is itself limited though, ideally I would like to reduce the output and noise by less than the minimum reduction permitted (ie make the effect less severe), but this is not possible and not likely to be possible because, unlike Octopus, Vaillant dont do remote firmware updates.

It will be costing me a bit (when it actually affects house temperature) to run NR mode at night, because it means that it will have to work harder in the morning to catch up.  It also displaces use from nighttime to daytime tarrif.  However in practice its only for a few days each season that the overnight cooling effect occurs so Im not too bothered.

Lets hope Octopus implement timed NR mode soon.

There WAS an official email issued, setting out that hush mode was merely a reduced output mode, and therefore of little value in winter. Ironically of course it is in winter when the pump is at its noisiest.

That is what everybody else's hush/quiet mode is so almost certainly, they cant do magic!.  See my comments above on how I successfully use Vaillant's equivalent  in winter which as you say is when its needed.  House dependent unfortunately

Yes, totally understand how you can manage the Vailant, and that output reduction is commonplace, it makes total sense. I like how you utilise it.
Octopus will catch up sooner rather than later. With a Cosy, hush mode is a simple on/off option, with no scheduling possible.

Which means that it can't be set for overnight use unless one sets a bedside alarm ⏰ 

i am not overly critiquing Octopus here, they do have room to improve the operability of the Cosy and it is promising that these little tweeks (remember the liwering of the minimum flow temperature a couple of months back) are introduced.