Hi there! I'm sorry to hear about this, but I'm here to help. Could you please respond to the following set of questions and try the steps?
What type of Nest Thermostat do you have?
Are you seeing any wiring report or error on the thermostat and/or the app?
Have you recently had service or maintenance on your electrical, plumbing, or heating system?
Have you tried any troubleshooting steps before contacting us?
How many zones are present in your setup?
Were there power outages lately?
Please check if the breaker switches are set to on.
Turn the breaker switches off and on.
Turn on manual mode by pressing the button in the middle of the Heat Link. No lights come on?