We have a 15-20 year old Goodman PGJ-042075-1A HVAC roof mounted unit. The warm-hot air stopped working yesterday. The fan comes on but, when it suppose to ignite the natural gas, nothing happens. We have lived here for three years and have had no past issues. I did a little research and had turned down the thermo below inside temp, then I shut the breackers the unit for about two minutes to re-set the system but, this did not help! Cold air still blows. Any help would be appriecated. Thanks