I have replaced the nozzle, cleaned the firebox with a vacuum. Also cleaned all the pipes from the furnace to the chimney and cleaned the chimney. I still have the flame coming out the porthole. Is there a clog between the firebox and the end of the furnace where the pipe starts?
Your heat exchanger could be plugged. Furnaces have portholes to access areas of the heat exchanger for cleaning. Boilers you have to remove the flue collector box to clean it. If you have a forced air furnace it could have a crack or hole in the heat exchanger in which case would cause backpressure when the blower came on. If this is the case the furnace will need to be replaced.
#1 turn it OFF. #2 call the licensed repair person in morning. #3 open your wallet.
