Lofty718

Dow corning 785 I wouldn't use anything else

You are missing the point, heat pumps shouldn't turn off once the heating demand is met because it means when they turn on they will need a higher flow temperature to acheive the desired result which in most cases means a lower COP and the heat pump having to work harder. I don't know any installers that use this setting, only as a last resort to fall back on. I run sensocomfort on my Vaillant boiler and still don't use adaptive, I don't want the boiler and pumps shutting down. I use less gas when on constantly and trickling a small amount of heat into the house. Curve 0.25 for UFH and 0.35 for the radiators

Adaptive is not the most efficient, when I have it turned on it has the curve higher than I would set it manually and tends to overheat the house Adaptive only works on the 'EXPANDED' mode which does not utilize weather compensation and low and slow heating, on expanded mode the heat pump will cycle more as once the heating demand is satisfied it will turn the heat pump off rather than the other modes that keep the heat pump on constantly never turning off when theres a heating demand and trickles low flow temperature heating into the house. Read the manual, all of this info is in there. An adaptive curve may be suitable for a small number of properties where you cannot get things calibrated properly with either full weather compensation (best option) then the second option would be active (weather comp with room influence modulation) .. expanded with an adaptive heat curve is the least desirable option for efficiency... but might work for some houses.

I have an unvented cylinder and a mixture of radiators and UFH. Many people have this setup and it's no problem at all to have one boiler that does everything, these installers sound like total scam artists trying to fleece you and the work is substandard, you should get rid of them and do not pay a penny more. Being qualified means nothing nowadays unfortunately, but you are in the right place now to get sound advice on getting it done properly

That's insane, why do you have another boiler i'm sure your system boiler alone would of been more than capable of running all the rads and the UFH!

Is your house fully UFH? if so then that is highly inefficient and you could run the heating straight from the boiler with no inteference from pumps and mixer valves (which are crap old technology anyway) This could of been a much cheaper install, by scrapping the mixer, pump and actuators and just getting a VRC720

Adaptive is the least efficienct setting, followed by active. The most efficient is using pure weather compensation but I run mine on active because things like cooking and solar gain can sometimes make the house overheat on pure weather comp

When a contractor quotes for piling it's an assumed depth just like most foundations. If they don't hit stable ground then they will drive the piles deeper until they do, they've done nothing wrong they are just trying to get on with their build. I do not see any issue here as long as they repair any damage to your property

19 thermostats is absolutely wild with a heat pump. You could probably remove every single thermostat and run the heat pump on weather compensation (how it should be) and your bills would be reduced by 30% at least My 5 bed 4 bath house is less than 200 sqm and feels pretty spacious, yours at 380sqm house must feel like a palace lol

The curves on Viessmann must be different, my flow temps are a fair bit higher than that. Always between 26-40

I run a curve of 0.25 for rads and 0.2 for UFH, over 1 is very high

I have a boiler and PDHW setup and keep my UVC at 42c. Works very well

Seems insane pricing A loft conversion like the OP's should cost around 60k in Greater London and the SE, not including flooring and bathroom fixtures

Does this flue flashing look right? all other examples I have seen it's much more integrated/tiled in, they are getting water dripping in through the felt

The coping stones should have a big enough overhang to stop that from happening