In my subdivision all the houses were built with either the G23 or G26 series furnaces. It seems they have a 6 year life span as probably 3/4 of all the houses have needed to have some form of repair this year. All the houses are 6-7 years old.
For what its worth you can find information, including wiring schematics, troubleshooting guides, flowcharts and more at the following link:
I have been working on repairing mine myself. I paid for a service call but the furnace still continues to malfunction. Almost everyone I call tells me that the Lennox furnaces are crap and even some parts stores dont sell Lennox parts because they say Lennox is a pain to deal with.
For the G26 series typical part numbers are as follows:
Main blower: 45H33
this cross references to emmerson motor model K55HXND-4565
average price I found $250
Induction motor: Lennox 49L5301
also listed as Fasco part number 7021-10841
this part ranges from $100 to $300 so look around to save money.
Flame sensor: lennox 40L81
Price $60.00 - $175 so again, look around.
Circuit board: Lennox 24L8501
Pressure switch: lennox 63k9301
You can also find some used items out there because a lot of my neighbors just replaced their whole units.
My advice... Dont buy Lennox if you have a choice. They dont seem to have a good reputation as I have witnessed a very high failure rate. Parts are available but you will need to spend some resonable time if you dont want to get robbed.
Dont bother going to the Lennox website either. Its about as useless as the furnace in my house right now!