I have a Concord 80 plus gas furnace and the blower fails to initiate, causing the burners to shup down after just a few seconds. :(

Check the flame sensor. It is a metal probe that the flame hits when running. This is a safety to prove ignition. The flame actually completes a circuit telling the computer that there is burner flame and it is OK to continue burning. If the sensor gets dirty it cannot complete the circuit just like a dirty electrical wire. Keep in mind that this is the metal probe with usually round ceramic at the base. It is not the larger ignitor. The sensor is usually on the left side of the burner box and the ignitor is on the right side. You can clean the sensor temporarily with fine sand paper but it is better to replace. Hope this helps.

By the way. I based my answer on the fact that you said a few seconds. If the flame burns for a minute or so and the blower does not come on it is either a problem with the circuit board or the motor is bad. You can check this by putting a volt meter on the board where the blower terminals are. White is common, black is cool (higher speed) and red or blue is heat. Put the leads on white and red or white and blue... which ever 1 is connected the heat terminal. BE CAREFUL THIS IS 115 VOLTS. If you have 115v after the flame shuts down you have a bad blower motor. The burner gos out because the high limit senses the internal temp of the heat exchanger is to high because the blower is not keeping it at a proper operating temp. After it cools down after a few minutes the burner will come on again.