I fixed that furnace myself!!

One of the most common problems I see is that the flame sensor needs cleaning. What is a flame sensor, you ask? The flame sensor is a stainless steel rod that has a ceramic base and on one side is the rod and the other is a wire that runs to the ignition board. This wire tells the board if there is a flame or not. Often the only thing needed is to take some sandpaper and clean the SS rod until it is shiny again. You can't hurt it by cleaning it because it is just a piece of stainless rod.

The syptom to tell you that that is the problem is: The furnace will cycle on and off several times and eventually will go into lockout (a state where the furnace will no longer try to light until it is reset). If you are experiencing this problem, try those steps. You just might save yourself a service call and be able to say: I fixed that furnace myself!