No, I get how to level up items. What I mean by "heat cap" is that my items have full heat and are ready to level up. What's bothering me is that the heat is still getting divided into them despite them being unable to gain anymore heat.
Since leveling items takes longer with the fire crystal system, I kind of feel that heat should stop dividing into the items that don't need it, just like they would if my items were level 10.
You have to use the forge. A little notification (star) will pop up when u can level your item (this will happen when in haven or at arsenal stations). You use fire crystals to level up. Or are you saying if your items heat level is 10 already? Sorry i'm confused by what u mean as max heat lvl.