Friday, September 17

New House Old Tech. Replacing a Danfoss TP9000 with a Nest 3rd gen.

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Me and my partner bought a new house and it took me ages to work out how the programmable thermostat works. So for ages I was looking buying a Nest Thermostat to replace the rubbish one the builders installed. I was even getting one for myself for Christmas, but ended up buying one of these instead!!

slideshow_4Screen Shot 2016-02-02 at 22.11.17Screen Shot 2016-02-02 at 22.10.39

Totally worth it, but back to my thermostat issues. Npower offer customers the chance to buy a cheap Nest for £129 compared to the usual £199 so thats what I did.

You may be asking, what is a Nest thermostat? And why is it better? There is a pretty good article covering smart thermostats with a bit on the Nest on Lifehacker. So rather than regurgitating, I suggest you click here and take a look. Essentially its a learning thermostat that can be remotely accessed plus some other things that I might write about once I’ve used if for a bit.


WARNING: Obviously it goes without saying, anything that is working with mains electrics should only be done by a competent person. This information is documentation of my personal experience and is provided without warranty. In addition, there is a disclaimer at the bottom too. I cant really say any more, be safe!

The first thing was to understand the current configuration of my system. Its a dual zone (I’m only using the Nest for the main zone) and hot water all heated by the boiler.

It is a Danfoss TP9000 thermostat and the wiring is as shown. The thermostat internally connects the L to a switches that then control the heating and water. In addition as shown in the wiring picture, I also have 2 live wires and 2 neutral wires. This is because the power comes from a switched fused spur and then goes to the boiler or maybe the junction box upstairs. Either way I know that black is to call for water and the grey is call for heating.

Screen Shot 2016-02-01 at 22.38.59Screen Shot 2016-02-01 at 22.33.00 Screen Shot 2016-02-01 at 22.36.24

So once I had worked out how my existing system worked, I needed to translate that to how the Nest works. Page 23 of the installation guide has all of the specifications for the switching contacts. The Nest differs in that it doesn’t internally connect the live to the switch. The image below is how I wired my old cables to the new Nest, the dashed wires are the ones I needed to add.

Screen Shot 2016-02-02 at 21.45.27

Once I had the wires figured out, I needed to actually connect them.

Issue 1 – Cable hiding

From all of the installation images, the cables are designed to come out of the bottom of the Nest. After posting on the Nest community board, someone responded with the idea to drill small 1mm holes on the back plate of the Nest within the raised circle and rounded slot.

For the round hole, I just drilled it out, started 3mm, then 6mm then upto 9mm. The rounded slot I drilled lots of 1mm holes and then snapped between the holes and for both I filled them smooth.

heat-link-and-boiler Screen Shot 2016-02-01 at 22.06.19

Issue 2 – Open cables

As you can see from the location of my thermostat, its in the kitchen. Actually its only about 200mm from the work surface. With the cables out the back, you can see a large hole at the bottom and my concern was that something (water, liquid, oil, food or anything else) could get into the 240V wires. I did think about designing and 3d printing something to plug the gap, but as mentioned before, my design skills need some work. So I just needed some plastic that I could put between the case and the cable clamp to block the space. Enter Chinese takeaway container! The plastic was actually a good thickness and once I got away fromt he edges of the container it didnt crack when cutting with scissors. So I cut some shapes that will plug the gap. Pretty easy, just fiddly and takes time. Remember not to tighten it too much, just enough to stop the plastic from bending.

2016-01-31 11.02.13 2016-01-31 11.04.54 2016-01-31 11.35.40 2016-01-31 11.51.55 2016-01-31 11.49.55 2016-01-31 11.50.34


Having made the modifications noted above, I wall mounted the nest and begun wiring.

2016-01-31 16.24.54 2016-01-31 16.59.42 2016-01-31 17.09.57

The images are dark and rubbish because for obvious reasons, I had no power. As you can see, apart from the wall needing painting, it went really well.

In regards to the actual thermostat we didnt want to wall mount the Nest, so I looked at the stand that they sell. Its about £30 and takes the circular mounting ring.

Screen Shot 2016-01-30 at 18.41.07  Screen Shot 2016-01-30 at 18.40.54 Screen Shot 2016-01-30 at 18.41.00

To me, £30 seems like alot of money considering its a bit of plastic. Luckily I have been working with a 3D printer at work.

My CAD skills still leave a lot to be desired so I went on Thingverse and downloaded the model Nest (v3) thermostat stand by jrd3n. Turns out its exactly what I was looking for! I snook it onto an overnight build I was doing at work and the next day I had a stand. This is how it turned out, I did have an issue with being impatient hence where it sits got damaged, but its not seen so I wasn’t bothered.

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Its worth mentioning that if you have access to a 3D printer then this is a really cheap option, but if you dont, find someone that does or buy the google stand.

Once I had the stand and installed the Heat Link, I was all ready to go. Final picture below 🙂

2016-01-31 17.23.09


I accept no liability for injury, death, accident or any consequential, incidental or commercial loss, however caused, resulting from the publication of material on this website. All electrical work, projects, diy jobs or work of a similar nature is carried out at the risk of the individual. 


  • Hi, thanks for posting this, I’m awaiting the delivery of my Nest v3 and have the same TP9000 but slightly different wiring (I have 3 Brown L instead of the 2 you seemed to have). Just checking about your added wires that you moved one of your L to 5 (common) on the heatlink and then connected 5 via 2 to L? ta

    • rdiver

      Hi Justin, so chances are, one of the L is coming in and the other 2 are distributing the power out. But without seeing its impossible to tell so be careful! If in doubt consult an electrician.

      With 3 lives you might struggle to get them all into the nest.

      If you have space you could use something like 2 of these connected together.

      and then all 3 wires into here and 1 single wire to L with a wire from L to 2 and then from 2 to 5.

      Hope that makes sense. Bascially you need to make sure that all the existing L are connected together.

      • Thanks, worked a treat. I ended up putting a junction box in place of the TP9000 as there was just far too much wiring for them to fit into the heatlink. Used a bunch of those wago connectors and have the heatlink in a better position with a 50cm 5-core extension cable.

  • Thanks for this Post its very useful. As another victim of the new build overly complex thermostat I will be looking to put in a decent one. I am looking to change it as soon as possible before I lose my sanity using the old one. I will be picking up my NEST this morning and will let you know how it goes. Have you looked to include the second zone yet which I would like to deal with at some point also?

    • rdiver

      Hi Tom, yeah I did look at it but it basically requires a second nest from what I understand. It wont however need the hot water which means an older generation one might be better.

  • Mike Watson

    Thanks for doing this blog. It helped me with replacing our TP9000 Danfoss (Programmer) and Danfoss TS2 (Thermostat) with Nest Heat Link and Nest Thermostat units respectively. Much appreciated

    • Hi Mike, out of curiosity, did you install your nest yourself? If so, any additional steps required for your particular setup?

      I have the same setup (Programmer & Danfoss TS2) and I’m toying with doing the install myself (not an electrician, but comfortable fitting new light switches and such in our house).

      Was initially hesitant due to the Danfoss TS2 Remote sensor which I was wanting to replace with Nest Thermostat, but I struggled to find out if it is a straight swap, but the comments here suggest it “may” be.

      Hope you can reply.


      • Adam

        I replaced my TP9000 with a heat link on Saturday and my TS2 with the Nest. My wiring was slightly different, I believe I had 3 neutral and one live. I used wago blocks to join my 3 neutrals, a bit of flex cable to join the wago to N on the heatlink. I had terminals 5 and 6 connected to my TS2 so I moved those to T1 and T2 on the Heat link and connected the Nest in place of the TS2 and it’s all working. Other than that I copied the wiring on this post. Not had time to properly play but heating has worked fine over the weekend and I have hot water.

        I know it’s too late to help you but hopefully this helps others. Props to this blog post too as I was lost until I read it. Next step is to replace my TS5000 with another Nest if I can work out how to wire in the second heatlink.

  • Chris

    All wired in, but noticed no hot water option? Now it is a 3rd gen Nest and I did include the call for hot water (Nest 6) cable and jumped live to 5. Should I have a hot water option (on/off) on the thermostat?

    It occurred to me that maybe my link cable from pins 2 to 5 may not be making contact properly (although it seems to be secure), if I’m supposed to have a hot water option, I’ll double check the pins tomorrow morning. I do seem to have hot water but it could’ve just been kept hot in the tank.

    Any ideas?

  • Chris

    Managed to resolve this.

    FIX: Go into professional settings change boiler type from combi to system boiler. Hot water option then appears and works.

    • rdiver

      Hi Billy, I’ll do my best to explain. The solid lines are the ones already there on my system. My understanding is that one live comes from the switched fuse and the other goes to the boiler, same for the neutral. For the nest, the principle is that 2 relays are used to switch live to the “call-for-heat” connections. On my system this basically sends 240v to a valve (or pump) that opens/starts.
      This means that the nest connections L, 2 and 5 all need to be connected to live. I added the dashed wires using a section of live wire from 1mm^2 twin and earth. The configuration shown allows me to only have 2 wires into each nest connection rather than 3 into the L and connecting it to 2 and 5.
      That image shows the final wiring.
      Does that clear it up a bit?

  • Rich McDermott

    Couldn’t have installed my best without the above guide, thanks!

    Did you have any experience of the heating not working upstairs? I have a second danfoss box upstairs which I took the batteries out of thinking it was redudant, is this correct? Anything obvious I might be missing?

    Thanks again!

    • rdiver

      Glad you found it useful.

      It’s likely that you have a dual zone system like us. We only use the nest to control our main zone that is everything except our master bedroom and en suite. The box with batteries is probably a second thermostat that controls the second zone. Our neighbours also replaced that with a nest too but we didn’t see the point as we never have it on.
      If you want to use the nest to control everything I’m guessing you would need to connect the 2 zones making the second thermostat obsolete. This is a bit out of my knowledge to be honest.

  • andy jennings

    thanks for the instructions

    the live link is what i was missing

    (very strange nest don’t mention it in their manual)


  • Gumbo

    This is the same setup as what I’ve got and I’m really grateful for the blog.

    I just have one slight difference to your setup.

    I don’t have the second brown live coming in and only have 5 wires in total

    1 x Live
    1 x Neutral
    1 x earth
    1 x grey for heating
    1 x black for water

    What would be you recommendation for getting my Heat Link wired up correctly?

    Many thanks in advance

    • rdiver

      Hi, everything is the same with the exception of the L wire. You would have the Live go to L, a suitable jumper wire from L to 2 and then another jumper wire from 2 to 5. Hope this helps.

  • Hi, can you help me with something? I have the same Danfloss unit as you, in a dual zone set up. I’m confused a little about the whole set up. My TP 9000 is located in my living room, the boiler is in the kitchen.

    Where does the heat link go? Am I supposed to intercept the wires from the Danfloss near the boiler, or would I put the heatlink where the Danfloss was?

    I originally presumed that the heatlink would go somewhere near the boiler, possibly in the same kitchen cabinet, and that I would then just replace the Danfloss unit with the Hive thermostat. I’m not that keen on mounting the heatlink on the living room wall.

    • rdiver

      Hi sorry this is probably too late. In an ideal world, I think you would intercept the wires at the boiler and then wire them into the nest. The problem is, you need to mess with the rats nest (in my case) of wires to work out which ones are which and then pull power for the nest from there. In order to make it an easy switch, I removed the danfloss controller placed the heat link in the kitchen as you can see from my post.

    • rdiver

      Hi Matthew, if you look up in the comments I seem to remember it requires a change of boiler type in the professional settings menu.

  • Josh

    I’ve got the same setup Danfloss TP9000 under boiler in utility room with thermostat in hallway. Am I right in saying thermostat will come off and Nest thermo will be a like for like swap. Then heat link installed in place of TP9000

  • James

    Hi Guys, I just have one question – hope someone can help – I also have the same setup, with two L wires in my Danfloss – does it matter which L wire goes into Heatlink L and 5 (as long as they are relayed with 2)?

    • rdiver

      In my case, I had no idea where the 2 wires went, I just knew that they all had to be connected together so that they were all live.

  • Dips

    Thanks for the the guide! I got my Nest working with this, so it controls the hotwater and heating. One issue is, there is a room thermostat from the old system still connected up – and needs to be ON a high temp for the Nest to work. Any ideas on how to get this out the loop? It is a 2 wire Thermostat.

  • 7esh

    Hi rdiver, I’ve followed the setup and pretty much have the same setup. The heat link switched on and seemed be working but the boiler is staying on some sort of constant mode and the heating was constantly on. Despite trying to switch on and off on the heating from the nest thermostat, it clicked but the boiler never goes off. And doing the same for the water, nothing happens.
    Have you had any similar experiences?

    • rdiver

      No I haven’t. I would guess that you are sending power to the boiler constantly and not passing it through the relay. The wires used for your system might be different to the plumber that installed mine. Did you take a picture of the wires before you removed them from the old thermostat?

  • Tom

    Thank you so much posting this. You are a legend. I have a clear picture and idea how to install nest in my home as i have same set up as you with dual zone.
    Out of interest could you please tell me why we have to change the boiler type from combi to system boiler??

    • rdiver

      Hi Tom, I could be wrong but I think a combi boiler heats hot water on demand and doesn’t have a tank where as a system boiler heats the water for the tank. So from memory if you have it set as a combi then you don’t get the option to schedule hot water heating for the tank as there wouldn’t be one on your system. Does that make sense?

  • R Hewer

    Thank you for this very helpful guide, got me up and running. My system had 3 neutral and 3 live wires joined at the TP9000 terminals, I’ve connected each set with a connector and run one neutral wire from the neutral connector, 3 new live wires from the live connector running to terminals L, 2 and 5.
    I also found and 3D printed this adapter for a 1 gang back box, may be useful to others:

  • Sunny


    I attempted to wire my 3rd Gen Nest today. I have a combi boiler and a Megaflo for hot water which is electric heated from what I understand.

    The old Danfoss controller only had 4 wires (Live, Neutral, 3 was for DHW on and 4 was for HTG on). I thought this would be a simple install of wiring Live, Neutral the the old 3 > 6 Call for heat Hot water, and old 4 > 3 Call for heat Heating.

    However when I turned the thermostat on I can hear the heatlink tick however it fails to turn the heating on.

    Would I be correcting in thinking I need a jumper from Live to 2 and 5 on the heatlink? Would this fix the issue?

    The final question I have is, although I have a combi boiler would I need to set this up as a ‘System’ boiler so I can get the hot water settings for my electric heated megaflo?

    Appreciate any advice.


    • rdiver

      Hi Sunny, you need to wire L -> 2 -> 5. Without this it will switch but the other end of the switch isn’t connected to anything. The danfoss did this internally but it needs wiring on the Nest.
      Yes if you have a secondary water heating element then you need to be on system boiler I would guess to be able to program it.

  • Aamir Quazi

    Wanted to thank you for putting the effort for this guide.

    Fitted mine today, but fitted the nest thermostat in place of my existing external thermostat using the heatlink 12v.

    Also copied your idea to protect the lower opening from water using some old containers.

  • Pete

    Really appreciate this guide and the comments. Helped me massively with my Nest install.

    I too had the 3 live and 3 neutral wires in the Danfoss, and from reading on here about the small connectors on the heatlink I decided to go the Wago route.

    I took the 3 existing live wires into a 5 way Wago 222. I took a new live (1mm cable) from the Wago to the heatlink L. I then took another new live into a 3 way Wago 222. From there I took 2 separate new live wires to the common terminals, 2 & 5. That way I only needed 1 cable per connector on the heatlink, and they were fiddly enough as it is.

    The 3 neutral wires followed suit, into a 5 way Wago 222 and then a new single neutral to the N connector on the heatlink.

    The hot water and heating calls went in their appropriate terminals and the remote sensor connected to T1 and T2 for the 12v supply to the hallway.

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