True blue furnace shuting off on t-stat but blower keeps running, limit switches check good. Shuting off power and turning back on results in normal operation. Doesn't happen all the time, what can I check next

Is the furnace control board giving you any kind of fault code? On most furnaces there is a light (usually red) on the control board mounted eiither near the burner or in the blower compartment. If in the blower compartment there should be a small window in the door through which you can view the light. Count the blinks then open the blower door. The key to the blink code should be on the inside of the furnace door or blower compartment door. Let us know what the code says & we can help you trace possible causes.