I've got a Goodman furnace that has served me well for 10 years. The heat exchanger has been replaced four years ago. I am now having a problem that I think is probably gas pressure or gas valve. the unit initiates, The vent fan starts and the igniter grows red. Gas is released and ignites, however the flame is dark blue and shut off immediately when the igniter solenoid clicks and the igniter starts to cool. This cycles three or four times until the unit lights and burns a bright blue flame. From this point the unit functions fine. This usually occurs between 6:30 and 7:00pm.