Suburban Hot Water Heater Issue.

Take the covers and burner tube off to expose both ends of the large (about 2 inch) tube that carries the flame through the water heater. It's just a big "U" tube that runs through the water and carries the products of combustion back out. It needs cleaning once it a while. The best way I know to do that is to run a rope through it so you can grab both ends. Take a shop towel type rag and tie it in the middle of the rope. Then drag it back and forth through the tube several times making sure it swabs the entire length of the tube. Then put it all back together and your nice blue flame should return. Wasps like to build nests in that tube and block the proper flow of gases. ANYTIME your water heater leaves a black streak up the side of your water heater, this is the thing to do to fix it.