Gas and Oil Home Heating Furnaces - Delayed Ignition

I have a 1974 Lennox Forced Hot Air Furnace(Model#G11Q5) and I will hear a gas explosion sound from it at start up. It doesn't happen all the time though. The gas company said it sounds like Delayed Ignition. What would cause this? How can I be sure that this is the problem? If it is the cause, how do I fix it?

Joe

Safety devices dictate gas should not turn on until ignition is working and energized. So I'd rule out the ignition process. I'd look at reason for gas fumes flooding furnace and no ignition right away until it buids up in the furnace, and then ignites with an explosion.

I'd say the burner in the area of ignitor or flame is clogged up with frothy stuff, rust, or ?. Then what happens is gas enters through other burner holes away from the ignition source and it finally explodes after the burner chamber fills up with enough gas.

Solution is to clean burners if my assessment is correct.

Hi Joe:

I imagine your furnace has a standing pilot? It sounds like the burners, pilot burner need a thorough cleaning. You'll need to remove the burner section to accomplish this.

Thank You. I inspected further and all the burners are producing equal flame. Also, it doesn't make the explosion noise all the time. Does that change things???

Also, how do you get the burners out w/out disconnecting the gas lines?

Joe

More than likely you have a spider in the cross over tube going from one burner to the next. It happens all the time. If your furnace has not been cleaned and safety inspected in a few years it would be a wise choice to get a trusted pro in there to do it for you. They should pull the burners and thoroughly clean them and the heat exchanger and inspect the heat exchanger for any breaches. Additionally they may need to pull the blower and clean it and check your safeties and flue pipe.