Finding software faults is a problematic activity in many systems. Existing approaches usually work close to the system implementation and require developers to perform different code analyses. Although these approaches are effective, the amount of information to be managed by developers is often overwhelming. This problem calls for complementary approaches able to work at higher levels of abstraction than code, helping developers to keep intellectual control over the system when analyzing faults. In this context, we present an expert-system approach, called FLABot, which assists developers in fault-localization tasks by reasoning about faults using software architecture models. We have evaluated a prototype of FLABot in two medium-size case studies, involving novice and non-novice developers. We compared time consumed, code browsed and faults found by these developers, with and without the support of FLABot, observing interesting effort reductions when applying FLABot. The results and lessons learned have shown that our approach is practical and reduces the efforts for finding individual faults.