I have a second generation Nest Heat Link System which has stopped working. The thermostat has a H71 error message on it. It is connected to the same power supply as the boiler, which is working.
I’ve tried to reset it by pushing the button for 20 secs but nothing is happening.
Any help would be greatly received!
I assume you have no lights on the heat link, and you state the power comes from the boiler circuit and that's working?
From your description and the thermostat being a 2nd gen unit, getting a spare part will be hard. They are well out of date now. Having said that, a 3rd gen heat link will work on your system, and you can find used ones on good old ebay.