Flames coming out the front of a warm air unit - the heat exchanger was totally blocked with soot
The old Balmforths are great for that. Went to one house and the guys was complainig all the ceiling in the house were getting a black stain to them, opened the compartment door and the wau case was black instead of white!. Removed the burner and stuck my brush up the hx and it was like sweeping a chimney, the pile at the bottom buried my hand and brush..... all from a poor pilot flame.