I HAVE AN OLD LENNOX FURNACE THAT I AM GETTING READY FOR THIS

WINTER. THE UNIT HAS THREE BURNERS. WHEN I FIRED IT UP LAST

NIGHT I NOTICED THAT THE CENTER BURNER FLAME WAS ALL AROUND

THE TUBE . THE TWO OUT SIDE UNITS WERE OK. EACH JET FIRED A

BLUE FLAME THE FULL LENGTH OF THE BURNER ( NOT AROUND THE

BURNER LIKE THE CENTER BURNER. WHAT IS CAUSING THIS AND HOW DO

I REPAIR THAT BURNER IF I CAN? ANY KIND OF HELP WOULD BE

GREATLY APPRECIATED . THANK YOU.