I found a post from another forum of why you might be getting RROD with secondary 0031 code.
Wilhelm_I: Might want to add this to your website?
So I'm 99% sure that the 0031 comes when the heat sink make contact with resistors on the motherboard (or maybe the bolts are overtightened). Sorry, but i don't have any picture for you guys.
My console is Xbox Elite.
If anyone has the same problem, try to solve the problem like I did.