I'm testing a system which used 1.5KE220CA-TP TVS diodes, running between 120 VAC L/N, L/G, and N/G. The datasheet indicates that the reverse standoff voltage is 185 V, and the minimum breakdown is 209 V. However, the diodes are becoming noticeably warm to the touch when the system is plugged in, and give off that vague burning smell.

Are these just sized poorly? What's a good way to choose diodes for minimum conduction here?

Thanks! (Sorry, the Digikey tutorial wasn't terribly helpful.)

edit: It seems like the consensus is that these diodes should be okay, and that there may be either slight heating due to leakage current, or heating due to unexpected transients. Thanks, everyone!