Hoping to find some help with a very cold house (in the UK, for what it's worth). Recently enough moved into a new places an electrician/plumber was fitting a new boiler and so was asked to install the latest Nest Thermostat. He is not a NestPro installer but said he had done this plenty of times.

Hear Link has been installed into the boiler, green lights for both the Heating and Hot Water Lights. The Status Light blinks blue, so connectivity issues with the Thermostat.

Page 1 of the 3rd gen instruction manual makes it pretty clear if affixed to a wall, the Thermostat should be hard wired into the electrics. If not affixed on the wall, it needs the Thermostat Stand to provide it with constant power.

My electrician said to ignore that, it can be charged and affixed to the wall unit and run off battery power for.months (just as the battery Nest Doorbell might).

I charged the Thermostat and then tried to affix to the wall unit. Initially looked fine and there was sufficient power to run through the WiFi set-up. When it came to search for the Heat Link though I received a H72 error message saying 'this thermostat is not receiving power' or something to that effect.

Is it the case that this electrician has screwed up, and that (as the installation guide suggests) the Thermostat has to be connected to power at all times? Or is there an easy fix here - if it requires constant power then why did it accept a charge and continues to have sufficient power to run through the WiFi set up and give me this error message?

Any help would be greatly appreciated as my (potentially dodgy) electrician is away for the Easter holiday!