My furnace quit working on me two days ago. After some troubleshooting, I discovered my glow ignitor was shot. Replaced that, new one works, and the furnace sort of worked. First burner lit for a couple of seconds and then quit. The other four did not light. The flame sensor is on the last burner so that's not the issue. Ok, so I was frustrated and when the burner lit again, I simply blew some air at the burners and voilà... the other four lit! Worked fine for about three hours, then all of a sudden, same thing happened. First burner lit, others wouldn't, I blew some air at them, they lit! Any thoughts? Is it something simple like dust blocking the gas? I am learning as I go so I understand that might be a ridiculous solution. But that one sounds cheap which sounds good to me. The furnace was installed in 1999 I think, Rheem Criterion. Any thoughts would be greatly appreciated. Thanks.

Your furnace needs to be serviced by a competent HVAC professional. Delayed ignition is nothing to play with.

Usually this is caused by

Dirty burners
Incorrectly aligned flame jumper area on the burners themselves.
Low or improper gas pressure adjustment.
Improper air shutter adjustment (if so equiped)
Damaged/rusted burners

Please take the necessary steps to make sure this repair is made ASAP. Unburnt raw gas can cause a very nasty situation especially if you are near the burners while trying to blow air to make them lite. A ON SITE inspection is the only way to tell exactly what the problem is. Before you hurt yourself or a loved one have it looked at by a professional.