Instruct: Classify the given Amazon review into positive or negative sentiment.
Query: on-off sensor stopped working

This product worked well for about two months of daily use, but then the on-off sensor stopped working causing the water to continue boiling until the electrical cord is unplugged from the wall outlet. While it is a nice, small kettle, it is inconvenient to have to plug it for use and unplug it afterward. I would have given it 4 stars had the sensor not malfunctioned.