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...
Thanks, it is **bleep**ed. Called the Nest customer services and they
have provided a replacement unit. I am just waiting for the electrician
to fit it later this week.