We have a Kitchen Aid cooktop and bought a 7 piece Kitchen Aid cookware set. Six pieces work fine, one does not. The 1.5 Q pan will not work on the cooktop. But it works on the Panasonic induction hot plate that we had purchased prior to getting the cooktop. It is magnetic and the concavity of the bottom is slightly less than the 2Q pan. I am guessing it is a manufacturing defect, but I cannot figure what it might be. Any ideas?
I have experienced something very similar, and it was because the pot was too small in diameter, so was not being sensed by the hob (range top). Higher end, professional induction hobs do not turn off as easily if the pot is pulled away for a second. Cheaper ones I have seen are almost on a hair trigger. So if your pot is small, and not perfectly centered, the sensor will trip and the range will shut off.
I expect the ferrous core is simply further into the pan (away from the inductor) and the range of the field differs between the two hobs.
That is, assuming you have already tried it on an appropriately sized 'ring' - if they're marked on the surface you should try to match with the base of the pan.
1.5 quart is not very large - could it be that it is a narrow pot?
Induction manufacturers tend to restrain their hobs to work with a minimum bottom diameter of the pot. If yours is narrower, it won't work. If it isn't narrower, but either the detection is shoddily implemented, or it curves up on the sides (I don't know if this is what you meant by "the concavity is less), it could be misrecognized as being too small.
There is no contradiction in it working on the other stove. Different manufacturers can choose different minimum diameters, or their recognition implementation can differ, so that even for the same diameter, one can recognize it as large enough and the other not.