Upgrading form Danfoss to Nest

21 Oct 2019
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United Kingdom
Hi All,

After scouring the web I thought I was up to swapping my current system over to the Nest Learning Thermostat, once looking at my own wiring I'm lost again. None of the examples I've found online have wiring the same as mine.

Currently have:

Remeha Avanta Plus Boiler
Danfoss ts715si
Danfoss TP5000 (x2 - One upstairs, one downstairs)

I'm looking to upgrade to the Nest Learning Thermostat 3rd gen, ideally the downstairs thermostat now and the upstairs later if that's possible.

This is the Danfoss ts725, located in the kitchen by the boiler:

And this is the downstairs thermostat:

And this is the upstairs thermostat wiring:

This is the Nest heat link wiring diagram, I'm not sure if I'm S-plan or Y-plan?
Nest Wiring.jpg

Any help would be much appreciated. If anymore information is needed just let me know. If anybody can guide as to which current wire numbers correspond to the new terminals that would be great!

Thanks in advance

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So the TS715i is a timeswitch for controlling the hot water, and the two Danfoss TP5000's will be controlling the two heating zones.

You will need two Nest thermostats and two Heat links, one for one heating zone and the hot water, and the other for the second heating zone. (yes, you can do this one later). Then some modifications to the wiring will be required to bring the first heating zone and the hot water control together at the first Heat link. It's not just a matter of moving a wire from one place to another. You will need to be electrically competent and understand how all of your system's components work and relate to each other fully in order to do this. So, unless you are really skilled, because this will be pretty difficult to explain over a forum it's probably best left to a professional to install.
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Nest e could replace your existing thermostat leaving the programmer as it is. So water not controlled by Nest e only central heating.

I am rather disappointed with my Nest, the Energenie MiHome TRV heads should follow Nest, however it has been rather intermittent. The thermostat as a stand alone works well, it is just the integrating with the thermostatic radiator valve which is a problem.

With electronic TRV heads there is no need to have zone valves to heat different areas at different times. So fitting a smart system you could remove the valves, they would be redundant, but I would say wall thermostat should be controlled by the TRV head, not the TRV head controlled by wall thermostat.
Whilst travelling home, I gave it some more thought and actually yours isn't too difficult after all :)

Locate the Heat link where the Danfoss ts715si controlling the hot water on/off times is (I'm assuming that is what it's for. If not, please advise what it does do) and move:

The blue wire in the 715 (N) to the Heat link (N)

The brown wire in the 715 (L) to the Heat link (L)

The brown wire in the 715 (1) to the Heat link 'Hot water common' (5)

The black wire in the 715 (4) to the Heat link 'Hot water call for heat' (6)

Insert a link between Heat link terminals (L) and 'Hot water common' (5)

Then transfer the cable from the downstairs Danfoss TP5000 to the Heat link. Connect the brown wire to 'Heating common' (2) and the black wire to 'Heating call for heat' (3)

You can wire the Nest thermostat to T1 & T2 to get the 12v to power it, or use a separate plug in power supply.

The upstairs Danfoss TP5000, can remain as it is for now.
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Stem this sounds good to me, it's exactly the info I need. I'll have a go tomorrow

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