Sometimes a furnace will give an error code suggesting that a high limit has opened, yet after checking airflow, temperatures and limit switches no issue can be found. This can be particularly mysterious when the error is intermittent.

At this point it is helpful to remember that bad solder joints on the circuit board can lead to this symptom.

Check the back of the circuit board carefully for cracked joints. The picture above shows a solder joint that would cause the limit failure code during overnight operation but would work perfectly during the day.

We have seen this issue on a few York DJ048 light commercial package units as well as other brand blower control boards.