Came to no heat call. system ran for about 4 mins then cut off. checked to see what error was being thrown, the error 33 was thrown. A Trane furnace code 33 typically means a limit circuit fault, indicating the furnace is overheating due to restricted airflow. So we we checked the filter, the Flue vent, heat exchanger, Fan motor, rollout/high limit switch, and burners. After testing the system we found that there was a crack in the heat exchanger. the customer will need to replace the heat exchanger in order for the system to operate properly. We also advise the customer to have an install supervisor come out to provide options for a new system