After I finished debugging the prototype, it required literally zero maintenance throughout the winter. Actually we were not living at the house at all, contractors doing remodelling work were living there instead. I installed a LCD screen with basic temperature controls and they had no problem with it whatsoever.

Doing this project from start to finish took me 2 or 3 months on and off, mostly during the weekends.

Doing it right yourself is the exact solution I arrived at myself :) I was shocked to discover how low the average technical level of local contractors is. I was super lucky to find a highly professional guy to overhaul the pipework, but anything more complicated I had to study on my own. Luckily, there is a ton of youtube videos, so the only thing you actually need is time.

Well done on the maintenance part! I think you are really helping me out a lot as I may not be up to the same level of effort for redoing our heating system.

It seems like this kind of think should be very doable in the industry but capability seems to be the big challenge.

Also do you have any concerns about software maintainability say 10-20-30 years from now? Can someone else pick up this system and run it if you sell your house?

Not OP but I have a lot of home automation. I did all of the work myself. It’s easy enough to swap the wall switches and the thermostat back to what came with the house.

A lot of my stuff is set and forget. Home Assistant doesn’t need to be updated or monitored. As long as nothing talks to the internet, all I need is backups of the config and spare SD cards.

Maintainability is a concern that I haven’t figured out yet :) Right now my plan is to replace my DIY thermostat with off the shelf device suitable for my boiler when we sell the house. All the advanced features will be lost, but this still is the average expected level of automation in the area :)