I've encountered the freezing inside bug. It's something they need to address, as radiators and ovens suddenly stopped generating heat, and all indoor areas went to 0C. Temp fixed it by buying land, but it's clearly a bug. Might also be able to clear it with save/reload, but haven't had the problem...

The same happened to me. Had a riot where 20 people got killed but managed to get the water system running. The heating system worked great until i started a new prison. The whole cellblock becomes blue (0ºC) after a while and the prisoners become quickly upset. I save and reload the game the heater...