I made a post about this bug 7 posts below (inexplicable heat in an air-tide room [outdated]), but it is not the core of the porblem. I think i found out what the problem is now.
To the bug:
I have over 100°C hot dirt spawning in my contaminataed water tank, which causes the water to boil into steam.
It has something to do with the Liquid vent. If I deconstruct it an reload the map it disappears, but if i place the vent again. it spawns again, even if i place the vent at an other location.
here is the savefile again: Heat.sav
Steps to Reproduce
I have no idea what causes the hot dirt to spawn. It seems to have something to do with the liquid vent.
This issue has not been confirmed by a developer yet.