What is the least likely reason why the blower motor does not start when servicing a gas burner?

The reason that it is least likely for the blower motor not to start when servicing a gas burner is due to the thermocouple not generating enough electricity. The thermocouple's primary function is to detect whether the pilot flame is lit and, if so, provide a small electrical current to keep the gas valve open. If the thermocouple were malfunctioning and not generating enough voltage, it would typically result in the pilot light not staying lit or the gas valve not opening at all, rather than directly impacting the blower motor's operation.

In contrast, a blown fuse would prevent electrical power from reaching various components, including the blower motor, making it a plausible reason for the motor's failure to start. Similarly, tight blower bearings that require lubrication would directly impede the motor's ability to run smoothly, thus preventing operation. A defective thermostat could lead to the system not initiating heating cycles, which would also indirectly affect the blower motor's activation. These factors are more directly related to the operation of the blower motor, while the thermocouple’s issues primarily concern the gas system rather than directly stopping the blower motor.