Last fall I had a similar problem. The furnace would try to start, but never ignite. Furnace code showed blower problem. I ran a flashlight on a stick into the outlet pipe. Found a bird's nest in the exhaust. Cut pipe and removed nest. Still would not work. Ended up taking the blower fan apart. Found the baby birds. Cleaned it all up and put everything back together. Works great. I added a screen to the exhaust pipe so that this does not happen again.