My furnace started acting weird about a week ago. The igniter sometimes works but after it hears to an adequate temp the blower keeps going blowing cold air in the house. Other times it will not even ignite but the blower comes on with the cold air again. The left light is flashing rapidly orange. I have replaced three heat sensors, the igniter and the vacuum valve piece that prevents the heater from working if there is a blocked exhaust at the advice of a friend. Still doesn't work and tonight it quit igniting altogether. We have also replaced the thermostat with no luck.