24 yr old furnace has multiple issues. Only blower was running when I arrived. Found that the temperature limit switch was unable to reset itself. Furnace is overheating due to age of equipment and dirt in the system that has accumulated. Combustion analysis shows higher levels of carbon monoxide in the flue vent. The drain on furnace has been disconnected and it dripping into a container that has to be dumped. Drain should be hooked up to a trap to prevent a vacuum that would keep the unit from draining properly. Also customer has issues with thermostat. Given the age of unit and multiple issues it is not recommended to repair. Customer is getting an estimate to replace unit today 1-3pm.