Which factor should be checked if the burner flames are not stable after ignition in an old furnace?

In cases where burner flames are unstable after ignition in an old furnace, checking the condition of the heat exchanger is crucial. A compromised heat exchanger can lead to improper combustion, affecting flame stability. If there are blockages, cracks, or deterioration within the heat exchanger, it may disrupt the airflow and gas mixture necessary for stable ignition and combustion.

A well-functioning heat exchanger ensures that gases can flow smoothly and that the heat is effectively transferred while maintaining optimal operating conditions. Any issues with it might lead to incomplete combustion, causing erratic flames. This importance highlights the necessity of a thorough inspection of the heat exchanger when faced with instability in burner flames.