I am having similar problems with my system, Error code 33-Limit Fault, & Error code 13-Limit Lockout. However, my system has been installed for almost two years and have not had problems previously. I did let the filter get dirty and did not replace it when I should have, and was getting errors (I don't think it was 13/33 but I could be wrong). I replaced it with a new filter (Filtrete 1000) and started to got 13/33 errors in the morning when it was heating the house from the setback. I finally replaced the filter with one of the cheaper blue ones from Home Depot, and I have not had any faults in the 2 days since I installed it. It would appear that the Filtrete was not letting enough air through and was causing the problem, does that sound correct? Is there something internal to the Infinity furnace that I can look at? I have not checked the outside air intake.. could that be causing problems?
BTW I just ran the furnace diagnostics (5 minutes in each stage) from the advanced menu and it did not get any errors.