Instruct: Classify Amazon reviews into positive or negative sentiment
Query: It doesn't work

I ordered this to keep the pipes on our external water heater from freezing. We live in Dallas, so it normally isn't an issue, but this winter has been extra cold. Got it in three days ago and installed it right away. For the last two days, the pipes have been frozen in the morning. We've had to thaw them out with a space heater. I'll be looking for a full refund.