I have a York Stellar gas furnace around 16 years old - model P3UCD16N07601A with an annoying starting problem - unfortunately it is intermittent. This is how the scenario usually goes when there is a problem. I call for heat, the system responds exactly as it should; it then runs for around 5 minutes then closes down. The (small) inducer fan continues to blow and the system goes into the re-try mode. Sometimes this will work and it reignites and continues to run until the temp has been reached but other times it does not and the inducer fan runs constantly. (I think it tries to reignite twice). If I then switch off the power and try again later it will sometimes work as required but not always. I read the manufacturer diagnostics which seemed to indicate that the White Rodger ignition unit had to be replaced which I have done. Unfortunately the problem persists. The diagnostics that came with the new igniter appear to indicate a sensor or limit switch problem. I just dont know where to start with this - any ideas.