My induction cooktop doesn't (always) detect the big diameters. It heats only the center of my frying pans, but works with the big saucepans, even though they have the same Ø :
Summit SINC2220 12 Inch Induction Cooktop with 2 Cooking Zones, 8 Power Levels, Automatic Pan Detection, Touch Sensor Controls, Starter Cookset and 220V
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