Thank you for the information @janethmsn. It is great to hear you already checked the power to make sure it is ok. If that all looks good try and power cycle the Heat Link, if you're comfortable in doing so. Turn the power to the Heat Link off for a few minutes and then turn it back on. See if it has any reaction after when you press the button on it.
Also let us check a few things:
1. When was the thermostat installed?
2. When did you first notice this behavior?
3. Was it installed by a Nest Pro or by a heating/electrical engineer?
4. Did you notice any message on the thermostat display?
5. Did you notice any power cut in the area before this occurred?
6. Did you have any maintenance done on the heating or electrical system recently?
7. Do you have only one or multiple Google Nest thermostat devices at the location?
