Product review (5 stars): I was doubtful, glad I was wrong.
This would be the second time my refrigerators water line had frozen up.  Years ago it took me days to find the little heater they make for that. But this time despite the heater it froze up. After wasting time I finally ordered this tool. I had the line defrosted in just a few minutes. I couldn't believe it.

The trick is the small tube. It gets the hot water to the plug of ice directly. As I injected the hot water the tube would advance. With in a minute I had melted the plug of ice.

You might think its a bit pricey fir a small syringe and tiny tubing. But you can waste a lot more time and money having some else do a service call.

Just make sure it is a freeze up, and not a faulty valve.  You can find lots of you tube vids on that.