After being idle for some time, my XB80 Trane furnace starts working like it should, gets the temperature to desired level, then shuts off. However, on the subsequent correction, when temperature drops below desired threshold (roughly 30 minutes after first operation), only the fan comes on, blowing cold air, and the gas never gets ignited. It continues blowing cold air since the temperature never rises to the set value. After rebooting the system via breaker, the furnace repeats the pattern. Namely, comes on just fine first time around, gets the temp where it needs to be, then fails to ignite on subsequent tries, turning only fan on. Any recommendations?

Usually the cleaning of a flame sensing rod is an easy task, can hurt nothing, & might help. If after doing that your problem persists, let us know & we can help you delve deeper.