Hmmm, I know you aren’t picking Jeff, it is a valid question.
Honestly i would have to answer with “it didnt feel right” in this case. There were no visible cues. I cannot say that I have any concrete data that I based that on. But I do generally run the ir thermometer over breakers, and most lf the time the temps are in pretty consistant ranges. Yes, AFCI are always higher. Breakers that have high load are higher, and no I cannot always comment on what has been going on with the breaker just before I tested it. So I understand it is not an exact science.
This one was outside of the range that my personal experience says is typical. That does not mean necessarily that it is broken. But common sense makes me question why a circuit that is not in use, that the homeowner is present and states that nothing unusual has been plugged in that morning, that is that much hotter than the rest of the breakers seems odd to me. Does it mean that I have detailed knowledge of every breaker type and brand and their operating temps? No. Based on the information I had at the time, it didn’t feel right.
Part of what I feel we do is offer the experience of the fact that we look at so many houses. I do not claim to have the most experience in my area, on this board, far from it I am sure, but it is what I have to go on. I am careful not to be alarmist and say “this is a fire hazard!! Shut it down and get an expert out here today!” But I think stating that this is not typical in my experience and may warrant further investigation by an expert seems a reasonable course of action and reasonable to say in our position. If I am wrong hopefully, I will find out and learn from the experience. If I am right, maybe I saved them some trouble down the road.