Burners need to be removed and cleaned annually.  There is a crossover path that needs to be cleared completely. The crossover path is where the gas flows, causing the other burners down the line to ignite. If the passage is not cleaned during routine maintenance, it might not allow the burner to light all the way across. This could cause the furnace to shut down, on a safety circuit. As Murphy's Law might have it, this will happen on the coldest day of winter.

Before removing the burners, take careful note of each burner’s placement.When you remove the burners, clean them by using a soft brush, to remove residue.  Some burners may be lapped over another burner. Improper placement of a burner may result in blocking ofthe crossover path.