My first thought is to carefully clean the box probe and try again. As for a test of the box probe, all I can come up with is stationing a remote probe as close as possible to the box probe and see if they agree or not; just be sure that the remote is accurate for boiling water at your altitude above sea level. It is not 212 degrees everywhere. Second thought is that the wood caught fire and the temp shot high. Other than that I would send Steve an email. Copy and paste your post and see what he has to say.