DamonHD

One rad change here retrofitting from gas to ASHP. Actually I should probably have bumped it up in size a bit further. But no other changes. For a new house I might well choose UFH at least in part, but that doesn't seem necessary.

A couple of visits to -5C here in sunnyish London have passed without incident for our ASHP. Flow temp got up to 47C... (I have 50C@-7C for one end of the WC 'curve'.)

If the embedded carbon/energy is a concern (and generally I don't suspect that it is for machines of this level of complexity), couldn't you gift it to a local gas spares place or GasSafe person for parts? When my combi was stripped out I did just that with the rather expensive heat exchanger that I'd put in just a year before, and the man was very happy. The sooner people switch to ASHPs and stop directly adding several tonnes per year of CO2 to the atmosphere via the flue, the better.

On my system am I pushing the weather comp curve down a few degrees (ie applying a setback to flow temperature, not room temperature) during peak: https://www.earth.org.uk/heat-pump-16WW-control.html#current I am actually on a flat tariff, but I did think about how I might make this work saving cash and carbon with Cosy: https://www.earth.org.uk/heat-pump-16WW-control.html#Cosy For our old gas combi I did indeed have the space heating entirely off for 4pm to 7pm.

Would a forced convector (ie with a fan) do a better job of distributing the heat?

Didn't see in there a link to NESO document: https://www.neso.energy/industry-information/connections-reform/connections-reform-results

Porous Tile Stain Dementia?

It optimises for occupancy, reactively and predictively, yes. Most people want lower temperatures while sleeping, but maybe not an icy room as they go to bed. That's effectively what Radbot aims for.

I agree that that fault mode is plausible.

There are solutions such as ... ahem ... Radbot, which don't need any particular central hub/stat and help manage the temperatures in each room automagically.

It may be @Pocster's WC seen from above with him on it...

https://www.gov.uk/government/consultations/feed-in-tariffs-fit-scheme-indexation-changes/changes-to-inflation-indexation-in-the-feed-in-tariffs-fit-scheme-consultation-document-html

By ensuring the that the system tells them just what they need to know to get there, and helps them along, assuming it's possible. ("Heat the house for zero cost with all the windows open when it's freezing outside" doesn't have a good solution!) And not expecting the end user to have a physics degree: "folk physics" seems to be bad in general.

By agency I mean "to make it do what the user need,s at reasonable cost" rather than necessarily "to understand each of the 50 control parameters". I had near neighbours who had a HP in new (badly built) social housing with no explanation on use, ending up with a ~£4k heating bill ~15Y ago. Agency would avoid that.

OpenTherm isn't open: I think you have to pay a lot to look at the spec and thus I haven't ever seen it. I suggested some time ago to LG and others that there should be a mandated basic common interface across all devices of a given type, but which does not prevent a manufacturer adding their features on top. Indeed this will be the final bit of my PhD research - how to give normal humans more agency with heat pumps than most ever had even with gas.