Came out to call. Customer stated that the system was working the other day, but now it isn’t. I checked system over and found the roll out switch for the furnace is charred. I tested system and found that the flame is rolling out on the first and second cell and is engulfing the burner compartment. The heat exchanger cells are rusted and deteriorating. The system is from 1999 and in serious need of replacement. Let owner of property know the hazard of running it, and that I strongly recommend that the package unit be replaced due to age and current condition. Gave customer estimates for a new package unit.