We perform low-frequency ac first- and second-harmonic resistance measurements and dc $I-V$ measurements on bulk FeSe crystals in a temperature range between 1.8 and 150 K and in magnetic field up to 14 T. We observe considerable second-harmonic resistance, indicative of nonreciprocal charge transport, in some samples. By examining the correlation between contact resistances and second-harmonic signals, we conclude that the second-harmonic resistance is not due to the genuine nonreciprocal transport effect, but is caused by joule heating at a current contact through the thermoelectric effect. Our conclusion is consistent with a recent preprint (Nagata et al., arXiv:2409.01715), in which the authors reported a zero-field superconducting diode effect in devices fabricated with FeSe flakes and attributed it to the thermoelectric effect.

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• Electrical conductivity
• Thermoelectric effects
• Iron-based superconductors
• Resistivity measurements