Responded to no-heat call on Ruud R95PA1002521MSA gas furnace in Vienna, IL during routine maintenance inspection. Diagnostic testing revealed restricted condensate drain line and failed condensate safety switch, causing system lockout. Cleared blockage with compressed nitrogen, cleaned condensate trap assembly, and tested float operation. Also identified failing flame sensor reading 0.6μA. Cleaned and tested sensor, now showing proper 3.2μA signal. Completed full system check with combustion analysis showing 94.8% efficiency. All operations restored to manufacturer specifications.