If the flame of the left burner in a furnace touches the heat exchanger only when the blower is running, what is likely the problem?

When the flame of the left burner in a furnace only touches the heat exchanger when the blower is running, it indicates that there may be an issue with how the heat is being distributed or contained. A cracked heat exchanger on the left side could allow combustion gases to escape or improperly mix with the airflow. This could cause the flame to be improperly directed towards the heat exchanger when the blower is operating and forcing air over the heat exchanger, placing additional stress on the unit.

A cracked heat exchanger can also lead to unsafe operation, producing carbon monoxide leaks or loss of heating efficiency. Ensuring the integrity of the heat exchanger is crucial for both safety and performance. Identifying this problem allows for further assessment and remediation to ensure that the furnace operates safely and effectively.

While other issues such as dirt on the burner or misalignment could contribute to operational problems, they would not specifically cause the flame to reach the heat exchanger only when the blower is running. Thus, the issue is most directly related to the heat exchanger's condition, particularly on the left side.