Hi @LorraineRutter , I am sorry to hear you're having issues with your thermostat. I would be happy to try and assist.
You mentioned the Heat Link unit seems to have failed. To confirm the LED lights on it seem to be off even though there is power to the unit, correct?
If so make sure to double check all breakers and switches, just to make sure it is all good.
If it all looks good try and do a power cycle on the Heat Link, if you are comfortable in doing so. Turn the power off to it for a few minutes and then turn it back on. See if it has any reaction after when you press the button on it.
Thanks for trying @LorraineRutter .
Let us check a few things next:
1. How long ago was the thermostat installed?
2. Was it installed originally by a Nest Pro or a heating/electrical engineer?
3. When did you first notice this behavior?
4. Have there been any power cuts in the area recently?
5. Has there been any work done on the heating or electrical system at the location?
6. Do you have one or multiple Google Nest thermostats at the location?