Be careful when reassembling:
Make sure the power button is put in the right way, it may look symmetrical but it's not! When put in the wrong way it does not work. Check if the shape of the button aligns with the edge of the casing, it's pretty easy to see if you pay attention to it.
Also keep an eye on the back camera. The round black cover glass may shift when trying to click the phone in its casing.
I ended up taking it apart at least 4 times because of this :(
Also, if you want to heat things up you can also use an incandescent light bulb and put your phone over it.