Fitting A Nest Heat Link

2 Oct 2016
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United Kingdom
Hi I'm a newbee, looking to install a Nest thermostat in place of the current manual room thermostat and was after a little information and clarification before I start.

I currently have a wall mounted mechanical Horstmann HRT3 thermostat which has x2 wires (which measure 12V on a meter) 1x Red wire in connector 1 and 1x Blue wire in conector 3. These both back to a jct box and change to 1x Brown and 1x Blue cables and go back to TA1 on my Ariston Combi Evo boiler which has a sticker no 240v on the connector.

With regards to Nest installation, my understanding is that I connect a 240v supply to the L + N connections on the nest Heatlink for power, and the x2 12v cables on TA1 from my boiler (Currently going my thermostst) , go to conections 2 + 3 on the Heatlink.. Then my new Nest Thermostat connects to T1 + T2 on the Heatlink..

I have attached a couple of photos of the current connections on my old thermostst, jct Box, and Boiler connections along with a wiring diagram for the Nest Heat Link.

pic4- Nest Diagram.jpg
pic1-Horstmann HRT3.JPG
pic2- Ariston E-Combi Evo Boiler.JPG
pic-3 Jct Box Mains and Thermostat.JPG
pic4- Nest Diagram.jpg

Thanks in Advance.. Regards Mark
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Much appreciated for the prompt reply. With regards to the Brown/Blue cables on boiler TA1 that currently go to the thermostat, do you know which would go to con 2 and con 3 on the heat link? Thanks
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Ok, thought as there was a 12v reading perhaps it mattered.. Many Thanks for the advise, appreciate the prompt feedback.. Regards Mark
im looking installing one of these thermostats too. I have the same boiler and old setup. did you take the power from the boiler or somewhere else thanks
you can take the 240v supply from the boiler or the outlet of the fused spur whatever is easiest,

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