Coleman gas furnace Model 7665-856, about 25 years old. Regulator and thermalcoupling and thermostat all replaced within last two or three years. Problem appears same as "THISAWAY" asked about 11/25/06. Furnace blows for about 45 seconds then shuts off. Burner appears to stay on when blower stops. Blower will come on after five minutes or so but continues to shut off after 45 seconds.