Rooftop heating tune ups. I replaced all the filters. I checked gas pressure, belt tension, temp rise and capacitors. I removed and cleaned the flame sensors. I checked safety’s, controls and connections. I cycled all units. * Rheem rooftop is displaying signs of unit failure. I repaired melted flame sense wiring and spark ignition wiring. I test cycled the unit and it is not currently experiencing flame roll out however I can detect the presence of aldehydes indicating heat exchanger failure. * I highly recommend replacement of the unit.