Assuming you have checked the power supply to the Heat link, and you have power at terminals L&N, then sadly I would think the Heat Link has failed! Can you confirm you have proved supply to the Heat Link terminals, and you have no lights visible? Should your answer be yes, then your next step is to replace the Heat Link!
Hi @svdmeulen, thanks for reaching out to us here. I would be happy to try and assist.
As @Frustratedddd mentioned, if the Heat Link shows no signs of life and you confirmed the power to it is ok, it may require a replacement. However we can check if that is the case together here. There are a few details I would need for starters:
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?