Comfortmaker enviro plus 90 furnace tripping high limit switch

[JJ 109]

Not sure if we do furnaces, but if so mine has started tripping the high limit switch that is on the burner. 
 

Did it once last year, and now recently has started doing it daily. it’s the type with a reset button. 
 

I have ordered a new auto reset switch, but would like to do some diagnostics and ensure nothing else is going on. 
 

thanks in advance for any help. 
 

 

[JJ 109]

I do not see a change in flame color or pattern when the blower kicks on, so hopefully not a leak in the burner.