A customer reports that when his furnace ignites, the flame rolls out in front of the heat exchanger. Who has the correct diagnosis?

The situation described, where the flame rolls out in front of the heat exchanger during ignition, is indicative of a combustion problem that can be associated with poor draft. Poor draft can prevent the proper venting of combustion gases, causing the flame to behave erratically or roll out. In functioning systems, the draft should effectively draw combustion gases up the flue and away from the unit, ensuring safe and efficient operation. A weak or reversed draft can lead to this hazardous condition, thus supporting Tech A's diagnosis of poor draft being a critical factor.

Tech B's suggestion that the issue is related to the limit control, while potentially relevant in other circumstances, does not directly address the specific symptom of flame rollout as described. Limit controls are primarily designed to prevent overheating and can shut down the furnace if it gets too hot, but they would not typically cause the situation of flames rolling out during ignition.

Therefore, the diagnosis provided by Tech A accurately identifies the root of the issue, focusing on the airflow and venting conditions necessary for proper furnace operation. Understanding this helps reinforce the need for thorough assessment and maintenance of draft issues in heating systems.