The Nest comes in two parts - the &quot;smart&quot; bit with the USB charger &amp; battery &amp; wifi, and the Heat Link - the actual radio control for your boiler.<p>The Heat Link has a big button on which lets you turn the heating on and off, overriding what the Nest is telling it.  That&#x27;s not as economical as a regular thermostat, but it means you won&#x27;t freeze:  <a href="https:&#x2F;&#x2F;nest.com&#x2F;uk&#x2F;support&#x2F;article&#x2F;How-do-I-turn-the-heat-on-if-the-Nest-Thermostat-isn-t-working" rel="nofollow">https:&#x2F;&#x2F;nest.com&#x2F;uk&#x2F;support&#x2F;article&#x2F;How-do-I-turn-the-heat-o...</a>