Circuit breakers trip two ways; magnetically, and thermally. A magnetic trip is almost instantaneous and is caused by a very high load like a short circuit. A thermal trip is from a smaller overload that heats and bends a bimetal strip inside the breaker that eventually activates the trip mechanism. There are hold-in, trip-out curves required for breakers that mean that a breaker must hold for a certain time, depending on the overload, yet must also trip within a time. The smaller the overload, the longer time for the breaker to trip and vice-versa. It sounds like your breaker was just doing what it was designed to do since the bimetal was cooling during the time the breaker you waited to reset it. Was there another fairly large load on the same circuit?.
Having said everything above, it is not unknown for a breaker to loose calibration and not act like is is supposed to do. This can be nuisance tripping, or failure to trip when it is supposed to do. If you are comfortable doing this, find another breaker (of the same rating) in your panel and exchange this with the furnace breaker and see if it still trips.
Originally Posted by Retiredrvbud
On a recent trip in our motor home which is a 99 winnebago chieftain we encountered a problem with our furnace. What was happening was every 10 minutes or so the breaker would pop and the furnace would shut off. After a couple of minutes we would reset the breaker and it would run again for another 10 minutes or so and pop again. Sometimes it would run a lot longer before the breaker would pop.
What could the cause of this be?