I have an older sears 600 series furnace that has four burners. One of the burners does not have a nice upward shooting flame. How do I clean the burner?

First you will need to remove the burners, if you can post a picture we can give you step by step instructions on how to remove them.

Why does the hot water furnace knock when the heat is on and does not knock when only the circulator is running? Is it possible the water is boiling? How can it be stopped?
JOA

JOA, you are better off starting your own thread if you want your question answered. It sounds like you may have air in the system.