For a given heat exchanger network (HEN) it is often necessary to determine its behaviour to disturbances in supply temperature and/or inlet flow rate variations, that is its ability, flexibility or resiliency to meet the design requirements at new operating conditions. An analysis of the HEN resiliency is very useful to assess other design options and for the design of a robust control structure. The use of design reliability theory coupled with fuzzy design uncertainties can be used to determine the possibility of violating the HEN constraints. This measures the potential of the design failure rather than the frequency of failure, the latter being measured by probability theory. The HEN constraints considered in this work are the target temperatures, hot/cold utility flow rate and heat transfer area/overall coefficient (UA). If the design under consideration results in a significant value of the failure possibility for any of these constraints, then this HEN design will require either a modification of the design or the establishment of a specific requirement in the control system. The case study treated in this paper shows that design reliability theory is a useful tool for determining HEN constraint violations that will require special attention from a control point of view, that is controllability analysis. Thus, this approach has proven to be a useful tool for determining design changes and for developing a workable control scheme for HEN designs. (c) 2005 Elsevier Ltd. All rights reserved.