PhilT

Damn I didn't see you!? The coldest average temp here in Jan was -3 when my heat pump used 38kWh in Auto mode. Previously when I used WC mode it would have been much higher. My house is a 90's build conventional brick/block cavity with around 10cm insulation, but only 130sqm so the OP's usage seems not as bad as he might think, notwithstanding useful tips being given above to improve efficiency of existing setup

Romania have their own rules based on building type for five different climate zones and it gets extremely cold in some of them - the mountainous ones where the R value requirement is most demanding. The AVERAGE night time temp in the whole of Romania in January is -6degC, so 25kWh per night for a 150sqm house is not bad with only 10cm of insulation, but what is on either side of that insulation, wood, bricks, blocks, how thick?

You are in "read only" mode. If you want to change any settings, from the FTC6 main home screen you need to press and hold the bottom left button for a few seconds. After that the domestic hot water settings window on the left in your last photo above will also show an edit symbol next to the two arrows in a circle. You should then also be able to change your WC settings. There are several YouTube videos on how to do this

I see Mitsubishi now offer an Ecodan R290 version but only up to 8kW, flow temp up to 75degC

You can get a rough idea of COP from the Melcloud app by looking at the "Reports" / "Energy Usage" charts, which give graphical results for input and output energy

Yes but Target Room Temp (Auto Adaptive) mode uses the WC curve as a baseline then overlays other forms of control - mainly varying the flow temp according to the difference between actual and target room temp, such that as target room temp is approached the flow temp is modulated until an equilibrium is achieved, allowing the longest possible heat pump runs. When you first start using Auto mode it takes a few days to "learn" how your room temp responds to flow temps, but eventually settles down to a steady state.

It's this thing https://les.mitsubishielectric.co.uk/products/residential-heating/control/wireless-controller-and-receiver To check flow temps and lots of other stuff I use the Melcloud app - both phone and PC version

There was another thread on this recently. I have an FTC6 controller and my understanding is that the lightning bolt symbol denotes that the hot water immersion heater is on. Is there some kind of heating circuit immersion heater - where is it - can you see it installed in the heating circuit somewhere?

Since November I switched to Target Room Temperature (Auto Adaptive) mode (was previously using WC) and my COP figures are better than last year (like for like average internal/external temps) by at least 15%. Furthermore the Mitsubishi Auto Adaptive software manages the heat pump operation in a more intelligent and efficient way to get the best out of it, for example gentler start ups, longer runs, automatic compensation for defrost cycles, with flow temperatures rarely going above 40degC even at -5degC outside. My FTC6 reported COP figures are Input Output COP Nov 483 2009 4.2 Dec 558 2342 4.2 Jan 698 2724 3.9 This is for an 8mm microbore fed radiator circuit with two pumps (primary+secondary) via a low loss header. Ecodan R32 11.2kW My house daily average temperature is 20degC +/-0.5 NB you need a Mitsubishi Wireless controller and receiver to be able to use Auto Adaptive mode

The RHI scheme doesn't forbid solar panels or wood burners with heat pumps, it just doesn't provide financial support for solar panels. It might for certain types of biomass

Your photo shows that your heat pump is currently heating your radiators (heat pump symbol bottom left). Hot water is "on" but in standby mode. There are several YouTube videos showing how to use this controller. There is one about the hot water timer - you could use that instead of leaving it on 24/7, that's what I believe most people do.

Yes that's what I do, for the same reason, mine's set to 19 during the day and 17 at night

How would you get any circulation without at least one pump?

Sounds like the solution is as per the conclusion of this Oct 28, 2021 thread - you need the latest software version 15. Assuming you have the Legionnairs cycle switched on, your Ecodan heat pump should take the DHW up to around 55 (flow temp max. = 60) when the immersion will kick in for the last few degrees, signified by the appearance of a lightning bolt symbol appearing in the FTC6 controller panel. But you should no longer see any other form of operation of the immersion heater unless you manually select hot water temp above around 55. I've switched off the LP cycle on my Ecodan - waste of time and money in my opinion.

How many litres per year, and was it an old (non condensing) or new (condensing) type?

Sounds like you either need stronger pump(s) or the settings need adjusting to allow higher flow rates from the existing pumps. Also someone I know with a similar setup to mine (two pumps) had three pumps installed (one primary, two secondaries)

SimonD suggested a 40l/min flow rate, so 33l/min, although very high compared to mine, may not be enough to shove water all the way around your big house and up into your loft K3! Do you have one or two flow pumps? if you have only one either it's not man enough or it is not set to a high enough speed. If you have two, check the other (secondary flow to rads) pump and increase its speed or, if not already, try setting to maximum speed. This should be quite easy as long as you can get access to both. Usually they have 3 speeds which can be adjusted via a dial or a button which selects 1, 2 or 3 lit LED's. You should be able to hear the speed increase.

I'm wondering if this (see photo) gets you the best of both worlds. The LLH (vertical black cylinder - capacity c. 2 litres) is connected such that only the primary flow (right top/bottom) can loop back around into the primary circuit. The LLH secondary return (bottom left is sealed off, instead rejoining the primary circuit return from the LLH further back downstream to the heat pump, thus eliminating any mixing of secondary return with primary feed.

yes - my rad and room temps were all over the place to start with, I think partly due to the glycol antifreeze gradually working its way through the system, and partly due to my microbore system, so I deliberately ran it hotter than needed continuously for as long as possible to resolve those issues. If you can't get it to work by running hot continously 24/7 with all rad valves open then (statement of the bleedin' obvious) you have other issues that need an expert inspection.

I had a similar issue on commissioning. I have a huge K3 in my conservatory and it's the furthest location from the source. I ran my system day and night for over a week, with all rad valves fully open, until temperatures reached a steady state within the spec ball park, which they did. So I would persevere, running 24/7 with all rad valves 100% open, then after a week if it's still not balanced you can start tweaking and/or considering other remedies.

Does the K3/loft air temp now meet your requirements?

have you tried bleeding the K3 in the loft?

So in summary the Grant 10kW R32 model would be ideal because it has a built in (unlike similar offerings) "HE Pump" which would be powerful enough to serve a simple single circuit UFH zone in a 160sqm single floor bungalow, without the need for a secondary circuit/pump/LLH/buffer

I notice some companies make a combined MVHR + heat pump of low capacity, presumably circulating warm air? Seems ideal in concept - what would prevent this from being a popular choice for a passivhaus?

According to the Octopus heat pump helpline there is no such restriction and the range 35-50 would be ideally suited to the new Cosy heat pump, though the key selling point remains the improved performance at higher temperatures, tech details of which have yet to be made public. Anyway as far as the OP is concerned I can speak very highly indeed of the Ecodan range, especially in full auto mode where I'm getting COP in line with what the databook tables quote - around 4.2 at 7degC, at 40deg flow temp.