Thanks for reaching out. I'll do my best to get this sorted for you as soon as possible.
Here are some helpful troubleshooting steps:
Press the button on the Heat Link and check if you have any lights on it
Check if the circuit breakers and the switches are set to on
Turn them off and then back on
Press on the button again and check for LEDs
Could you also help me with some answers to these questions?
How long has your thermostat been installed for?
Did the issue happen during the installation?
Is there any error on the Nest thermostat display?
Have you had any power cuts recently?
Have you had any work done on your electrical or heating systems recently?
If yes, was the power properly restored at the fuse board after work was done?
How many zones are present in the setup?
Yep, all fixed thanks and the broken unit has been replaced. The challenge is not the replacement process, it is getting started and having to dig around on forums like this to find out what to do. Once I had the customer services number all was well. That needs to be up front when you search, 'Nest heatsink not working'.