My Carrier Weather Maker 8000 furnace isn't working properly. I can have the furnace set to about 70 degrees, and it will get 65 degrees in the house, and the furnace will not go on. When it does go on, it stays on for about 15-20 seconds, and then it shuts down. I have to unplug it for about 20 minutes. When I plug it back in, it works fine for one cycle, then it starts acting up again. Per a certified plumber, I've replaced the filters, the limit switch and the thermostat, but still nothing. Please let me know what needs to be done to get this working properly. Also, where can I get a replacement manual for this furnace?

When it shuts off, look at the controller board for a blinking LED. It should blink a 2-digit code. That will help to determine what is wrong. I've attached a representative listing of the codes.

Best of luck,
WallyH