This bench top computer controlled service unit enables the operation of the Armfield range of small-scale heat exchanger systems. It provides controlled cold water flow, bi-directional hot water flow and the instrumentation required to do a series of in-depth investigations into heat exchanger performance. The individual heat exchangers can be quickly changed over, to enable comparisons between different types of heat exchangers to be made. The HT30XC requires a personal computer with USB for the operator interface.