What do you have to do to get the furnace to restart?
Do you have to push a reset on the furnace itself or do you have to adjust the thermostat?
There is a flame sensor in your furnace that will shut down the furnace if it does not see a flame. The sensor works on a timer. When your thermostat contacts close (or gets to a preset temp.) it sends the signal to your furnace motor which pumps fuel through a nozzle and ignites electrodes to burn the fuel.
If the flame does not ignite for some reason, the sensor will shut down the whole unit. This keeps the fuel pump on the furnace motor from continuing to pump raw fuel into the fire box.
If the flame sensor shuts down the furnace you will have to push some kind of reset button on the unit before you can try to start it again.
When your furnace goes out if you just have to adjust the thermostat to get it started it's probably the thermostat.
If you have to push the reset on the furnace itself it's something with the unit. Could be it just needs servicing (nozzle cleaning, electrode adjustment, etc.)
Spanky