Tucson guy's half right, heat isn't the real issue, tracing is.

That "cup in his hand" thing is real, the coffee is almost beside the point.

Getting a straight answer out of a tech is half the battle, and it sounds like this guy actually earned his $89 instead of using it as a sales pitch. That part about the cracked igniter and dirty flame sensor is real stuff too, those are cheap fixes that a shady company will blow way out of proportion to scare you into a whole new unit. The filter tip alone saves you money, so keep that company's number handy and skip the $6,800 quote places.