I am having a intermintant problem with my furnace, I came home the blower was on no heat , I checked the themostat setting - ficked the service switch off and on a couple of times- burner started, I can hear the burner when it comes on, the furnace ran all day without problem I wake in the night same thing blower running cold air go down fick the service switch burner comes on is thia a transformer problem? There is plenty of fuel in tank