I have a Payne 394GAW (about 1987, no standing flame,electric ignition). Starts fine and burns 3 to 4 secs and recycles. Classic dirty flame sensor problem. I cannot find a flame sensor to clean. I have removed burners and looked throughout. Is it in the ignition assembly? Is there some other flame sensing device? What else could be the problem? The pilot and gas seem to work fine. Thanks