I have furnace that uses fuel oil and is power vented. The home is only 17yrs old. I recently had a tech out due to the furnace not working. He replaced the ignition source and the furnace has been working since. However, I am worried there is a problem. The home is warm, but I have been noticing that the furnace will turn on run for a period then turn off leaving the blower going. After the unit cools down, while the blower is still throwing warm air, the furnace will come back on and continue to heat until the house reaches the desired temp. This will happen once or twice during a cycle of running. Essentially short cycling and leaving the blower activated. Should I be concerned, is this a pending issue or fire hazard? I contacted the tech and he said it was just an internal thermostat regulating the cabinet temp. Did he adjust the unit incorrectly when he serviced it or is he correct in stating I should not be concerned? What happens if that internal thermostat fails?