How are you providing a 'basking spot'?

If your temp reads 87 on that dial without the 'basking spot' there's a good chance the temps are well over 100 degrees when it's on. That's going to lead to the end of your snake in a pretty short time. Read the care sheet and make the appropriate adjustments, then leave the snake alone for a few weeks and when you go in there and he hisses at you, ignore it and pick him up anyway.