This paper presents a non-contact method for making relative measurements of the resistance of surface mounted resistors. An application of this technique is in automatic test equipment, i.e. within the limitations of resolution and accuracy of the measuring system it is possible to detect if incorrect resistor values are mounted on a printed board assembly. Measurements are made on two specially designed test boards. Two different measurement systems are used of which one is based on thermopiles and the other is a heat camera equipped with a QWIP (Quantum Well Intersubband Photodetector) detector. The detection of a minimum change of resistance, corresponding to a change of approximately 5 mW in dissipated electrical power, was achieved. Simulations of resistor board systems using; THERMIC 6.6, THERMICPCB 6.6, and Flotherm 3.2; and a dissipation power model are presented as a demonstration of predictions of the thermal fingerprint of a circuit board.