Abstract: A thermal difference detector for testing serviceability of a heat source includes a sensor connected via an amplifier-filter to a microprocessor outputting an indicator. The inventive detector can be used in a system for testing the serviceability of a plurality of heat sources. The system comprises a plurality of detectors, a robotic structure, with the detectors mounted on arms of the structure, a microprocessor and an indicator unit. A method is also disclosed comprising a sequence of steps including detecting radiation from an ambient temperature source, detecting radiation from the heat source, transforming them into electrical signals and processing the signals, comparing them to each other, and making a judgement of the serviceability of the heat source based on a predetermined criteria.