90 % furnace, burner box is hot to the touch and manual reset has tripped once last week, is it possible the inducer mtr. Running to slow? Why doesn't the pressure switch open if this were the case? Pvc pipes are clear..

Ansr. To question: secondary ht. exchanger is accumulating deposits of what looks like kitty litter and reducing the ability to remove hot gases from unit, had to pull top collector box cover to prove and clean out.