Google Nest Thermostat Troubleshooting Steps

How to manually turn heating on or off when
your Nest thermostat can't connect to Heat
Link
If you can't control heating with your Google Nest thermostat or the app, the Heat Link and
thermostat may be disconnected. You can press the Heat Link's button to turn heating on and off
until the connection is restored.
Press the button on your Heat Link to manually turn on heating:
Nest Thermostat E: Press Heat Link's button twice

3rd and 2nd gen Nest Learning Thermostat: Press Heat Link's button once

Press the button again to manually turn off heating (press twice for Nest Thermostat E).
Keep in mind:

Manual heat mode will continue to heat your home until you manually turn it off, even if
you reconnect your thermostat.

If your thermostat controls hot water, your hot water will also turn on when you turn on
manual heating..
When manual heating is on, your system won't follow your regular schedule. It also

won't be able to follow other thermostat settings. For example, if you have an
OpenTherm compatible system, manual heating mode will not allow your boiler to
modulate water temperature..

You can only turn on manual heating if Heat Link is disconnected from your thermostat.
Otherwise, use your thermostat or the app to control heating.
Trouble shooting Steps