While it might have worked as advertised here by accident, I don’t really believe this was how it was ‘;supposed’ to work.
If there ever was a time peoples beliefs were so strong they actually would put their hand in boiling water thinking god would save them then the priests would have believed this as well, and used actual boiling water as a result.
The situation sketched here only works is the priest doesn’t actually believe in the divine ordeal and is just trying to scare the suspect into confessing, but in that case the suspect would probably not be sure enough of the miracle either.
