Installing nest thermostat

[Nickclarke2183]

Well that explains how I went wrong. Will take a look tonight after work and see if I can decommission that wiring.

Not a clue how I'm going to get a wire from the nest to the thermostat but that's another issue all together. Fun times

 

[stem]

Often DIY installers plan to use the original room thermostat cable to provide the T1 & T2 link between the Heat link and the nest thermostat, and then find that whilst the thermostat end is in the correct location, the other end is not near the Heat link anyway, so have to extend or reroute it.

The nest thermostat doesn't need mains cable to connect it to the Heat link, because it's only 12v, thinner cable such as that used with security alarm systems, or data communication is neater and can be easier to install and conceal.

I once managed to pull an old thermostat cable out of the wall from upstairs, terminate it in a junction box to maintain the integrity of the circuit, and then drop some thinner security cable I had on hand, from the Heat link down to the thermostat in its place. It was a 4 core cable, so I put two cores in T1 and two cores in T2.

 

[ericmark]

Even as an electrician I found I needed to draw out what I have to be able to work out the wiring, maybe just me with too many turns on the coil, at 68 not as fast working things out any more.
The wiring diagram included the boxes be it the heat link or wiring centres, clearly yours will not be the same, and likely a lot simpler than mine, but showing an idea not a plan for you to follow.

Once it is laid out on paper or PC you can see any errors, and work out how best to use wires already there. There are normally four areas.
1) The boiler.
2) The programmer. (Normally some where with easy assess.)
3) The wiring centre. (Normally around the airing cupboard, but in my case with the boiler.)
4) The thermostat. (Often in the hall, in my case wifi linked to hub and TRV heads.)

When I came to do mine, I found triple and earth cable from hall to utility room, in the utility room I found a programmer and fused connection unit and other end of the triple and earth cable from hall, with a further triple and earth cable going it turned out to flat below the house, however only two wires connected and they changed colours so clearly some connection I am still to find.

The motorised valves, pumps and boiler all in the flat, so there were only two wires between flat and main house, so I moved the location of the programmer/heat link to flat and used a mains supply from flat instead of house, this then allowed me to use the two wires for T1 and T2.

And this is the point, I planned it all first, it took time to draw the plan, but a lot less time than trying to pull in extra cables. Unlike the programmer where it needs to be where you can access it, the heat link can go anywhere, it did not matter that it was under the main house in the flat.

So as stem says, the programmer supplied the thermostat the thermostat would have controlled the motorised valves, and then the valves the boiler, this has changed to some extent as the thermostat now controls the heat link, so they have swapped around, heat link controls motorised valves, then motorised valves control the boiler.