Best guess: there's an underspec'd mosfet on the hotend that failed on contact with reality
This is the worst case scenario. No, not that this shitty printer nearly lit itself on fire; that I've got like fifteen ideas on how to diagnose the core problem but I won't have time to even look at it for days
DO NOT BUY A CR-10S. It ships with thermal runaway protection switched off. Mine started toasting its extruder on first heat. The interface is such that you can't easily monitor the temperature when you're in another menu, and if they're still using PTFE in the extruder, it's going to poison you as well. Fuck that. Bad, dangerous product.
Won't get a chance to really dial it in for a few days, but it's here. First impressions: it's going to need a ton of work, but might be sweet once it's up and running.