After a major remodeling project, I had my air ducts cleaned and a furnace check-up. Nothing reported wrong. Since then, the furnace has failed to fire three times (over two months). I flip the power switch to reset and it fires right up. I had the HVAC firm that did the cleaning and check-up come out the last time it happened, without resetting the unit, and they could not find the cause, stating "since the furnace does not have a diagnostic system, I can't find the reason that it won't fire". This concerns me that a certified technician can't fix a furnace because the furnace can't self diagnose itself. He recommended a new furnace. All of these discussions were with my wife.

The furnace has worked fine for the 6 years we have lived in the house, and it only started acting up after the "cleaning and check-up". Furnace is 14 years old and we believe it had the inductor??replaced in 1995.

Any suggestions on root cause?
Jim