A long time ago in Kings Lynn I was working on the site where we were building the bypass. Sitting in my portakabin a Hilti nail came through the wall behind me and kept on going past my head and through the wall in front. It had come from an office 2 doors down.
Some of the junior engineers...
We have mains pressure hot water with a solar heating system. They are quite common in France.
It's just a tank with 2 coils in it. One for the glycol passing through the solar panel and one for a hot water bleed from the log burner/central heating. It also has an immersion heater for cloudy...
This may not be completely applicable in your case as you need to repaint, but oven or BBQ cleaner will get it off. I spent a very uncomfortable 3 days recently cleaning 200 years worth of wood soot off my limestone inglenook fireplace. Oven cleaner, kitchen roll and a stiff brush worked...
Sounds like the way it's done in France. We had 2 years to replace the sand drain system with a compliant micro station when we bought our house. Some of the cost (about 10k€ if I remember right) was taken off the cost of the house.