I have a 1983 Ruud Deluxe 90 plus natural gas furnace. I can get it to turn on, makes a click noise and then the flame turns on. I have 4 pipes that light up with flame, one of the pipes the flame does not go all the way down the tube like the other 3, and it like spits the fire back towards you, towards the cover of the furnace. What is causing this? How do I fix this?