Getting the Nest Learning thermostat (3rd gen) to work with A 'Worcester 24i Combi' bolier! Help Ple

10 Sep 2018
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United Kingdom
Hey! I have bought the Nest Learning thermostat (3rd gen) I have t he heatlink and the nest linked and connected and the heat link connected to the boiler.

There area that I am struggling with is that the controls from the to my boiler don't work.

My boiler is 'Worcester 24i Combi'

My thermostat controller is 'Danfoss TP5'

The boiler has a inbuilt time.

Currently the options for my boiler is this:

Mains - Neutral, Live,

Fuse - 2A SLO-BLO,


PROG - Neutral, INPUT, LIVE.

STAT - Neutral, INPUT, LIVE.

I currently have it wired like this:

T3 from the heatlink into live from the stat - This doesn't seem to make it work.

Any advice or help welcome. If any information or pictures are needed i'll try and add them later on tonight! Thanks in
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The Nest provides both time and temperature control, so the current thermostat needs to go. You can't have two thermostats controlling the same boiler. Note where the existing wires at the TP5 go, and remove it. The terminals should look something like this. Terminal 2 won't be used.



1) The wire currently in the TP5 terminal 1 (com) goes to the Heatlink Terminal 2 (Heating Common)

2) The wire currently in the TP5 terminal 3 (on) goes to the Heatlink Terminal 3 (Heating Call for Heat)

3) You need a 230V mains supply to the Heatlink N & L terminals to power it. If it is not available already at the TP5, it needs to come via the same 3A fused supply that feeds the boiler. So can be connected to the L & N load terminals of the boilers fused spur.

4) The the existing boiler inbuilt timer should be set to be permanently 'on' 24/7 and the Nest will take over the time control.
Last edited:
Thanks for the reply stem!

I will give this a try tomorrow and hopefully it will work!

Currently I had it set up to the 230v combi boiler in the screenshot below (i think). The picture shows the terminals for the boiler (if it helps to picture it) and the option I tried to do.

I did take out the stat and wired it as the 230v. Currently the TP5 is wired Live and Input. Just for my own sense of mind, are you referring to follow the second diagram (in the picture) - 'Low voltage/dry contact combi bolier'?

When I did try it yesterday, the nest unit did communicate with the nest link but wouldn't control the boiler :(.


  • Boiler.jpg
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Heatlink terminals 2 and 3 are just switching contacts, so will switch whatever voltage they are connected to, either 230V mains, or low voltage. The only difference with the 230V Nest drawing is that the 'L' is provided from the Heatlink's 'L' terminal. This is fine and would probably be normal for new installations. However, as your wiring is existing and is already connected to a 'live' at the boiler, it is getting it from there already. Below is a sketch of what I described in my first post.

Nest Heatlink 2 Model (1).jpg

You can proceed as above and that will still be fine. However, having now seen your wiring details, instead of running the 230V supply from the Fused Spur, it may be easier for you take it from the boiler's wiring terminals instead as below. However you should only use this method if you can access your boilers wiring terminals without having to remove a room sealed cover to do so.

Nest Heatlink Model (1).jpg
You don't have to wire the Nest Thermostat to the Heatlink T1 & T2 as I have shown, you can use a separate plug in power supply for it if you prefer.

When I did try it yesterday, the nest unit did communicate with the nest link but wouldn't control the boiler :(.

Did you have the existing boiler time control set to be permanently 'on'?
Did you have a live connection to Heatink terminal 2?

For it to work, the answer to both of these questions should be 'yes'.
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Thanks a bunch stem! This has worked a treat for me! Many thanks! The second picture is the one I did and it worked :).

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