There are three ways to connect a thermostat to a boiler. 1) Connecting to the boiler ebus, but hive does not have that option, you would need Nest, but be aware just because it says thermostat does not mean you can use it with Hive. 2) Extra low voltage off/on often 24 volt, you can only use this with a single channel Hive. 3) Low voltage control (230 volt) do remember in USA they have different words for voltage bands, so with USA designed gear low voltage is really extra low voltage, but with 230 volt control either single or duel Hive can be used.
This assumes connecting to a boiler, often the thermostat connects to a motorised valve which in turn connects to boiler.
So if 230 volt control you need 4 wires in the cable, 230 volt line in, 230 volt line out, neutral and earth even though you don't need to connect the earth to Hive, the cable has to be there.
With Hive duel channel the link is fixed, but with single channel you need a link Line to Com.
Some boilers to access the terminal box means breaking the gas seal so has to be done by gas safe, yes I think it is silly, as in Wales if fitted in a kitchen it also needs a Part P scheme member so can only be fitted by a mutli-skilled man or needs two people. But it seems some boilers are made that way.
I like the Idea of Hive, I actually have Nest, but think the idea of the TRV head sending a demand for heat to the Wall thermostat is great, and using that in theory does not really matter where it is mounted, as yet not found anyone with full system fitted, would love to know if it works?
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