Replacing old thermostat for Nest

miguel · Mar 29, 2022

Hi all,

I want to replace my current thermostat with the Nest Thermostat, but wire labels don't match.

My boiler is Worcester Greenstar 24i Junior combi boiler, which is on the back of the wall where the thermostat is.

Photos here Another Nest Themorstat (3rd gen) question - https://www.diynot.com/diy/threads/another-nest-themorstat-3rd-gen-question.589322/#ixzz7OwWUl9Jb

Any help massively appreciated, thanks!

Basher · Mar 29, 2022

The Nest Heatlink requires a live and neutral supply.
Your existing thermostat is wired to control the switched live to the boiler. There appears to be no neutral present, as if there was it would be wired differently.
It will need a new 3-core plus earth cable to be run from the Nest Heatlink to the boiler.

I don't know if the mains wiring connections to the boiler are accessible without removing the casing, you may need a gas safe engineer to do this.

However if the current thermostat cable goes to an accessory or wiring centre, rather than directly into the boiler, you may be able to reconfigure the wiring outside the boiler.