Atwood Furnace problems

Your fan should run for a few seconds prior to ignition to evacuate the chamber of gas. then it should openb the selenoid gas supply and try and spark. One of 2 things could be happening; either your fan is not running (part of the cycle) prior to ignition, or the selenoid to open the line to ignite is not opening. Once it's on it heats a thermocouple to sense flame to keep the selenoid open until the thermostate sends the signal to close. Any one of these parts could be failing or operating out of sync. resetting it could be resetting the cycle thus allowing only one cycle. That would be a board issue. That or your lines need blown out. Heck it could even be the furnace itself is heating a connection to the point of loosening, and then when it cools it closes enough to get current. In any case, if it's a warranty item, let them figure it out.