Nest Gen 3 installation - replace controller?


5 Jan 2016
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United Kingdom
I nearly bought a Nest Gen 2 and would have been quite happy installing the Heatlink where my current thermostat is but now they have brought out the 3rd generation which has HW timer as well as CH I have some installation questions.

I have:
Ideal Minimiser SE boiler
British Gas UP1 controller (aka Drayton LP112)
British Gas RS1 room thermostat (aka Drayton RST1)

Can I install the Heat Link to replace the controller?
If so what should I do with the old room thermostat?

I have uploaded pics of the controller wiring and switch settings.
image.jpeg image.jpeg

Thanks in advance.
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The 3rd generation nest heatlink, is designed to replace an existing programmer. It is provided with 3 extra terminals for hot water control. These are numbered 4 (HW Satisfied) 5 (HW Common) and 6 (HW Call) for the switching functions. The wires in your existing programmer presently going to terminals 1 (HW Satisfied) and 3 (HW Call) would be wired correspondingly, with the heatlink 'common' terminal being connected to a live supply.

From the existing wiring, it looks like your system has a 3 port motorised valve (Y Plan) which will be switched by the existing room thermostat. So, the wiring to the existing room thermostat should be removed and the Heatlink terminals 2 (CH Common) and 3 (CH Call) would be used to perform the motorised valves switching functions instead. This may involve some rewiring of the current installation. A simpler arrangement that some may suggest, (I don't recommend it) would be to connect the existing RST1 thermostat switch wires together (L and 3) so that it is by-passed, and the heatlink would use the existing wires at the programmer, but this is not seen as being good practice because unused electrical equipment / wires are left in situ and still live.

If your wiring utilises a wiring centre (often in the airing cupboard next to the hot water cylinder) it may be possible to make this link at the other end of the cable, and remove the existing room thermostat and wiring.
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Thank you stem for this very useful, detailed and considered reply.

I haven't noticed on the Nest site the simple phrase '... 3rd gen heat link designed to replace an existing programmer... '. It seemed to me that it is, so thanks for the confirmation of this and for the wiring tips.
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I agree with freddos comment, but I can't help thinking that nest perhaps deliberately make it difficult, in order to encourage you towards having one of their approved installers do the work.

Having said that, most UK heating systems that utilise motorised valve(s) and separate thermostats for heating and hot water, whilst the wiring connections are generally pretty much the same, they are often installed differently, depending on how the components are physically located to each other, so unless you understand what wires carry out what function, and how they relate to each other, it can be quite difficult for a DIYer, to work out how to install new controls. For this reason it's not possible for a manufacturer to give one definitive installation diagram for all situations, and for this reason, professional installation is probably the best for most people.
Good point. Most of the links take you to their installer pages.

I do take the wiring for granted as I work with it so much as an electrician. I can also picture the connections easily in my head which makes fault finding much easier. I know of several electricians who can't follow central heating wiring diagrams, or suddenly start to panic if they see loads of wires. It must be much worse for a DIYer!
I bit the bullet and ordered the Nest 3rd gen from Amazon, duly delivered this morning.

Following stem's guidelines and, with careful preparation and various notes, I have successfully installed the heat link to replace the programmer and then paired the thermostat.

I was a bit disappointed that the heat link case is set up for bottom entry - I had to carefully drill out the case for rear entry - and also it is too wide for a standard pattress, so I had to drill holes in my kitchen tiles, always a nerve wracking experience for this DIYer :).

Maybe that's why there is no reference to replacing a programmer within the Nest site?

Thanks again for 'holding my hand'.
but I can't help thinking that nest perhaps deliberately make it difficult,

Nests manual is a technical document, like most heating controls manuals, such as honeywell etc, it is designed to be read by people with the technical knowledge to understand controls for quick reference not a held by the hand step by step guide, of course diy'ers need a step by step detailed instruction...not saying it is right or wrong just the way it is.

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