Cleaned & checked gas furnace. Inspected heat exchanger & flue venting. cleaned burners & flame sensor. Checked voltage & amp draw of motors. Test capacitor. Checked filter. Tr41. Adjust Blower: 2.3A. Inducer: 1.03A. Adjust Gas pressure: 3.5 inches water column. Temperature rise: 55 . Supply: 122. Return: 67 . Found basement pressure negative (-.01 inches water column) due to leaks in return-air ducting. This is causing downdraft of flu and fluegas spillage at water heater. Suggestions: recommend installing make-up air venting into basement from first floor.