I could see that turning the power shower to its hottest could result in in painfully hot water, but if it's producing scaldingly hot water (hot enough to give second degree burns) then that sounds like a dangerously and illegally defective power shower. If I were you, I'd check with the CAB about what your options are.

Anyway, that said I hope that you heal up quickly.

Have some nice safe e-hugs, since they're much less likely to hurt than real ones.