Lenox G12 cracked heat exchanger common?

[Liceaga]

Our service tech told me that the Lennox G12 has a history of cracked heat exchangers? I don't know if this is only the 60,000 btu model or if he meant other nodels as well. Have any of you experienced this?

[HayZee518]

If the flame is not adjusted properly it will crack the heat exchanger because of hot spots within the combustion chamber.