This paper provides an overview of a study completed which aims to increase WEC system reliability by using numerical tools to quantify load uncertainties at an early stage of the wave energy converter (WEC) design process. A case study that applies the variation mode and effects analysis (VMEA) methodology to a load assessment exercise for a reference WEC is presented. A first step in the methodology is the identification of uncertainty sources in the load assessment, considering the design basis definition, the numerical modelling approach and the post-processing methodologies applied. Simulations were conducted in WEC-Sim for a wide range of scenarios with the aim of quantifying the identified sources of uncertainty. Results from the case study presented indicate that the post-processing methodology applied when deriving ultimate limit state (ULS) metric can be responsible for a high degree of uncertainty in the ULS results. In future work, it is recommended that additional investigations are conducted to assess methods of identifying the most appropriate extreme value distribution to apply (e.g. through a goodness-of-fit parameter). This study was conducted as part of the RiaSoR 2 project.