Most burners in a boiler are a ribbon type that need to be removed annually for inspection and cleaning.

When the burners are removed, keep a note of where they came from, especially the burner with the pilot light bracket on it. After you have pulled the burners, inspect them for cracks or rips in the burner itself. If there are any, replace the burner. Clean out the burners with a light brush by running the brush inside of the burners. Vacuum the inside of the burner box to remove all dirt. Also clean out the pilot assembly. If you have a spark pilot, lightly sand the flame sensor.  When reinstalling the burners, make sure they are alllevel so they will light evenly. If there are any burner crossovers, make sure they are overlapped. Some burners might need overlapping in order to light the one next to it.