No heat at the time I arrived. Cycled system. System would not light up due to obstruction in venting. Tryed to check intake venting with camera, could not find obstruction. Removed intake venting and vented intake to basement. System fired as normal. Checked heat exchanger, found it very rusted and damaged. Cracks starting to form. Ventor motor bearings are very worn. Igniter is in very poor condition. Burners are very rusted and damaged. System is in very poor shape. Checked CO and XS air in exhaust. XS air is high at 198. Clogging secondary heat exchanger.