We've had a Nest 3rd generation thermostat for 12 months now. In this time, the thermostat's wifi chip fried so they sent a replacement. Now the Heatlink broke leaving us without heating when it's 7C outside. It will take a couple days for the replacement to arrive. Not to mention the hassle of having to bring in an installer to replace the Heatlink which you can't replace on your own like the thermostat. I wish I'd read the reviews here before buying the product. If anything breaks again after our warranty expires in a few months we'll just throw it away at get something else!
