What might a technician suspect if flames "roll out" when the blower is energized in a standing pilot furnace?

When flames "roll out" in a standing pilot furnace, especially when the blower is energized, it typically indicates an issue with combustion safety. In this scenario, a technician would suspect a cracked heat exchanger. A cracked heat exchanger can disrupt the flame pattern and cause combustion gases to escape into the area where the burners are located. This breach affects the proper combustion process, leading to abnormal flame behavior like rolling flames or even flames escaping the burner enclosure.

The presence of a crack can also lead to insufficient airflow or improper venting of combustion gases. When the blower is turned on, it can create a draft that exacerbates these issues, potentially allowing combustion gases and flames to leak into unintended areas. Therefore, the observation of flame roll-out serves as an important warning sign, suggesting that the integrity of the heat exchanger must be assessed to ensure safe operation of the furnace.

Other issues, such as blocked vents, dirty burners, or low gas pressure, can cause other symptoms but typically wouldn't result in the same immediate and dangerous flame behavior when the blower activates.