Turn off the heat with the button at the bottom click on the save it explains more.Btw here is the original so you dont think the nuke is weak btw turn back on your heat button.
Ok, that is because: 1) the temp is already set high, and will not change temperature 2)The heat is automatically produced from the reaction of the neutrons. it returns to normal. It doesn't even effect anything with heat sim off, other than what the lava would. essentially, it is exactly the same at low temp as it is at high temp with heat sim off.