Way more to it than that. Just because the light blinks and says something is acting up it doesn't mean that part is bad. It will certainly point you in the direction of the issue but its not going to tell you exactly what is going on. You can have a code for ignition failure and think ok flame sensor but is the gas valve opening? Is the igniter glowing? Are the burners even lighting during the start up sequence? Lets say the igniter isn't glowing. You assume the igniter is bad but did you check to see if the board is sending power to the igniter?Flame sensor diagnostics:
1)Find the blinky red light
2)Count how many times the blinky red light blinks
3)Refer to the chart to find out what that number of blinks means is wrong
Diagnostics of a furnace is bit more involved than just looking at a blinking light.