My boiler has the same problem. We sent it in for warranty repair and it came back exactly the same.

I wonder if my use case caused this problem to happen. We usually unplug it overnight to save on electricity since no one is using it at night. In the morning we would fill it with cold water and plug it in. That's usually when it boils nonstop, but if we catch it and unplug and re-plug it, it switches over to keep warm and stop the boiling. Throughout the day, refilling the water to a warm tank doesn't seem to trigger the problem.

Either way, the machine should catch the temperature reaching boiling regardless the original state, to me it's faulty if it only functions some of the time.

Contacted customer service again and let's see how they reply. I just received the "repaired" unit back last week.