I turn the heat on the thermostat to the automatic heat position, and the furnace will lite for about 5 seconds then goes out. When I turn the power off and turn it back on, the furnace will once again come on for about 5 seconds then go off. The entire time the fan is running, even when the flame is out.\

You might try turning off power remove and clean the flame senser real good with fine sandpaper or steelwool and replacing,, just a little labor could save a service call sometimes