My furnace starts then when the burner starts it shuts down?

Hi elm and welcome, have you tried cleaning the flame sensor? You can use fine sandpaper and carefully clean sensor and sometimes get a few more years use. Good luck and let us know how it goes.

Does the heater LED blink any code? They will be found on the inside of the heater door. Possibly a flame sensor but could be one of the safeties too.