" no heat. have a york D2NA018 thru 048. I turn heat on and turn up thermostat and no air comes out of the vents. If I turn the fan from auto to on I get a weak flow of cool air from the vents. I went outside to look at the unit, and I can hear a fan or blower running in the unit.(fan on thermastat is back on auto) I open the side of the unit and can see the pilot is not lit, and the small blower unit in the top left is not on. Unit is propane. Any help? is back to auto)"