Hello !
I am an auto mechanic, so when it comes to furnaces, I know nothing, but I have been learning about my furnce today.
I have a goodman GMP-150-5 furnace that when the thermostat turns it on, I haer the draft fan start and run and after about 5 minutes, it just shuts down.
Now, I looked at the ignitor which looked fine, but since it was not glowing and this is a common part, I replaced it with a new one (That was no help).
I checked the fuse on the circuit board (good), and found out about the diagnostic codes. (The diagnostic code is flashing 3 blinks - would this cause these symptoms with the draft fan running and no ignitor glowing ?)
I am going to remedy the problems shown by the diagnostic code, but I am unsure if there may be another problem since the ignitor is not glowing and I have 2 children coming home from school to a home with no heat, so I want to make sure I don't replace anoher part un-necessarily and still not be able to make it run.
Thanks to anyone who answers this!

Look on the inside of the furnace blower for the code's or blink code. It will tell you the most likely place to start.

Thanks for your help !
There has been some progress - I cleaned out the bottom of the chimney (dirt nearly blocking the flue). The new problem is the ignitor now glows, (It didn't before) but no gas flame.
I did a little poking around with a continuity meter and I found one of three heat sensors (don't know if this is the right term? ) has no continuity through it (This is a small metal unit with 2 wires on it, there are 3 of them mounted by the burner - one on top and one on each side-the wires run through all 3 of these, and it ends up at the gas valve).
Since 1 of them was defective, I jumped across it and everything worked, but the burner got so hot it started melting the wires above it.
Is this still a draft problem ?
Thanks for any help!

You bet it is and right about now you should be calling for a On Site inspection from a professional before you destroy the furnace and possibly yourself.