Field-programmable gate arrays are susceptible to radiation-induced single event upsets. These are commonly dealt with using triple modular redundancy (TMR) and module-based configuration memory error recovery (MER). By triplicating components and voting on their outputs, TMR helps localise configuration memory errors, and by reconfiguring faulty components, MER swiftly corrects them. However, the order in which TMR voters are checked inevitably impacts the overall system reliability. In this study, the authors outline an approach for computing the reliability of TMR-MER systems that consist of finitely many components. They demonstrate that system reliability is improved when the more vulnerable components are checked more frequently than when they are checked in round-robin order. They propose a genetic algorithm for finding a voter checking schedule that maximises the reliability of TMR-MER systems. Results indicate that the mean time to failure (MTTF) of these systems can be increased by up to 400% when variable-rate voter checking (VRVC) is used instead of round robin. They show that VRVC achieves 15-23% increase in MTTF with a 10× reduction in checking frequency to reduce system power. They also found that VRVC detects errors 44% faster on average than round robin. Nomenclature Symbol Definition N number of TMR components in the system Ck component k, k = 1, …, N O kn Ck is observed for the nth time by checking its voter(s) Δt o time period between successive voter observations (assumed to be constant for a given system setting) Δt dk time period between two consecutive observations of Ck Δt rk time period to recover a faulty module of Ck Δt k total time period over which Ck can fail Δt di j time period between successive observations of Ci and Cj Δt d′i j average time period between two consecutive observations of Ci in the interval between two consecutive observations of Cj IET Comput. Digit. Tech.