About me

read first – disclaimer:

I am not a professional electrician – some of the products used here are not EU certified. I am under no circumstance responsible for any damage nor injuries one could

experience by trying out my documentation.

I have bought 2 Nest Thermostats… and I am just about to connect one to my 220v natural gas heater (not a 24V native one to be clear).

I am in Greater Paris (France), and I intend to share my experience with you by posting simple schematic, tutorial, Q&A

stay tuned…


P.S: as you can see I have never blogged… so this blog does look ugly (suggestions are welcome)

80 Responses to “About me”

  1. massimo December 23, 2012 at 16:20 #

    can you ship me the RC840-240 in italy?
    i would buy it.

    • usingnestineurope December 24, 2012 at 09:17 #

      Ciao Massimo,

      I am happy to arrange this – due to the holidays please contact me when comes 2013, after January 3rd please.
      happy holidays to you and your family!


      • Feridoun August 6, 2013 at 19:11 #

        Hi Matt
        Do you have any more of the Aube units for sale?

      • usingnestineurope August 7, 2013 at 08:21 #


        Thank you for your inquiry and yes i do have a few extra units,
        However it will be September before i can arrange any shipment


    • usingnestineurope February 24, 2013 at 14:19 #


      thank you for your inquiry – since I am not familiar with this Siemens Thermostat, please confirm from the manual you sent, on page 13 (of 14) which connection diagram your system is currently setup please?

      also, what is your heating system made of please? Natural Gas…?

      thank you

      • bart February 24, 2013 at 14:21 #

        i am not sure, i haven’t taken it off the wall yet, the heating system i believe is radiator in floor blown up, i am wondering if the nest will be able to control the fan speed like the siemens? my next chance i will take it off the wall to see what kind of wires are connected

  2. bart March 1, 2013 at 15:17 #

    ok here is a pic… http://imgur.com/oQeVDUZ

    now what? lol

  3. Francesco March 25, 2013 at 15:42 #

    If you are interested, I built a system to adapt NEST in Europe to locate time zone and weather in Europe http://www.nested.eu

  4. Nested.EU (@NestedEU) March 25, 2013 at 15:45 #

    If you are interested, I built a system to adapt NEST in Europe to locate time zone and weather in Europe http://www.nested.eu

    • usingnestineurope March 25, 2013 at 16:24 #

      interesting service you’re providing… first time I see this.

      • Nested.EU (@NestedEU) March 25, 2013 at 18:40 #

        Thank you, is to try. I made a link to this blog because I think it did very well.

      • usingnestineurope March 27, 2013 at 09:13 #

        I am interested in running a trial, so please provide me via email my login/password and I will run a test will then in return consider a post on my blog.



      • Nested.EU (@NestedEU) April 3, 2013 at 13:54 #

        Register for free on the site and send me an email to support@nested.eu making your request.

  5. bart March 25, 2013 at 18:42 #

    here is my nest got it working in europe


    • usingnestineurope March 25, 2013 at 21:05 #

      Hey hey very nice mr Bart !

      Tell us more about your heating system please, brand,energy used,
      Which country are you in?

      Are you renovating or building your home from scratch?


      • bart March 25, 2013 at 23:01 #

        yes i posted my original thermostat earlier http://imgur.com/oQeVDUZ

        Siemens RDF310/RDF410

        its a new apartment in poland

        the siemens has a 3 speed variable fan speed, Q1, Q2, Q3. Y11 is the heat, so this is how i wired it:

        -both L wires to aube Black
        -both N wires to aube Blue
        -Y11 heat + Q2 medium fan speed to aube Red

        so when i turn the heat on, the fan comes on automatically

        and then from aube to nest the 3 wires, RCW to Rc C W1 that was easy

  6. Nelson July 4, 2013 at 02:55 #

    Hi. I live in Australia and most of the heaters here are gas based. I measured the voltage across the two cables coming from my unit to the thermostat and it happens to be 5V DC. When I short them, the heater comes on so all I am hoping for is that the NEST shorts the Rh and W contacts without worrying about the voltage on it. For charging and other operations of the NEST thermostat itself, am planning to use an external transformer.

    Wiring design I had in mind is
    a. +ve wire from the heater and +ve wire from the transformer connected to Rh.
    b. -ve wire from the heater connected to W.
    c. -ve wire from the transformer connected to C.

    Picture – http://db.tt/ggYu693C

    With the above, I have made the following assumptions
    a. The Nest will get its power from the Rh/C circuit.
    b. It will control the heat through the Rh/W circuit.
    c. Due to no connection between W and C, the gas heater will never get 24V AC.

    Sorry am not an electrician so please pardon any incorrect terminology I may have used or if any of the above is totally wrong.

    I would really appreciate everyones feedback.

    • usingnestineurope July 4, 2013 at 08:15 #

      Hi Nelson,

      this is great to see folks from around the world unleashing their creativity as a lot of people are craving for using
      Nest in their respective homes.

      from my first glance at your schematic, what is obsviously missing in my opinion are means to block your 5V DC from getting into your 24V AC power supply. The easy way to do this is to insert so called DC blocking capacitors in series on each leg of your 24V AC wires (going to Rh and C connections). this will prevent from your boiler to be shorted.

      I have personnally have made Nest, in my early phase of trial/errors, work from 24V DC and it seemed to be working.for that matter, I actually used a simple lab’ DC power supply between Rh and C.

      I will have some more thoughts on this and over the week end see if I come up with some idea to amend to your drawing in a constructive way.


      • Nelson July 9, 2013 at 11:13 #

        Hi Matt,
        Hope you have had some more time to think about my project. Meanwhile, I have been doing a lot of reading and found some very useful resources which I thought are worth sharing for the benefit of all –

        1. http://www.doityourself.com/forum/thermostatic-controls/465126-help-installing-nest-millivolt-system-using-24v-transformer.html

        2. http://ask.metafilter.com/206318/Help-Installing-Nest-Thermostat-on-Millivolt-System-Using-24v-Transformer

        Both of the above forums have testimonials of people connecting an external 24V AC power supply as per the wiring design I mentioned in my previous post. Just wondering how there will be a voltage leak between the AC (transformer) and DC (heater) since the circuits will be independent.

        Some people suggest using a SPST relay. Depending on the answer to my previous question around voltage leak, it may or may not be needed. Diagram – http://s1206.photobucket.com/user/hvactechfw/media/millivoltsystemandnestthermostat.jpg.html

        Also, please can you confirm how many amps the transformer needs to be to operate the NEST?

        Looking forward to your response.

      • usingnestineurope July 9, 2013 at 21:04 #


        great findings on your side – and in my humble opinion – those solutions will work!

        what I meant previously was that you connected a DC and an AC path together which was likely to damage your boiler/furnace.
        with the use of this SPST, it isolates both sides while allowing NEST to get both its supply voltage,but also its ability to trigger the SPST.

        on top of my head, the current into NEST was in the range of 40 to 80mA (but I could re-measure it) – the short story is that a low power transformer will do.

        if you have a multimeter, set it to “DC Amp” and I would insert it in series between your furnace/boiler and your current thermostat.
        trigger the thermostat and read the current on the meter. this will help you select the SPST – to make sure that it carries the current thru the 5V DC leg.

        Does this help some?

  7. Nelson July 10, 2013 at 00:18 #

    Thanks for your prompt response Matt. Much appreciated. The question around amps was more so for the new transformer. I emailed NEST support overnight and they have advised ‘Nest can only work with up to 3 amps. Anything above that will cause damage to the Nest.’ Does this sound right? What amp rating does your transformer have?
    Am assuming I don’t need to worry about current between my existing furnace and thermostat as I am not going to change anything on it but instead just introducing an external transformer for NEST. Please feel free to correct me if I am wrong.

    • usingnestineurope July 10, 2013 at 06:33 #


      The 3 amps feedback, in my opinion, pertains to the current rating built-in the switch of the Nest itself.

      So going back to the diagram you found, to me it suggests you want to select a transformer with less than 3 amps on its secondary ( the 24v side of the transformer). I think 1 amp will be largely sufficient.

      Note i didn’t experience this issue personnaly and here is why:

      #1 my Gas heater had a 220v line and neutral supply built-in

      #2 so i used this, together with the rc840 to have my 24v supply built and at the same time have this spst .

      #3 if i recall the current flowing on the 220v supply lines was fairly low, a few mIlli amps

      • Nelson July 13, 2013 at 09:41 #

        Thanks for your response Matt. I visited a transformer specialist yesterday and explained what am looking to do. He was not clear on what the SPST relay does so I said it was meant to prevent voltage leak from the transformer to the furnace/heater. The next question now is whether the SPST relay is meant to close the loop on the load side when the coil is energised on the coil side. He said that was what a standard SPST relay is meant to do but just wanted to make sure that with NEST in the picture, it would all work. I’ve drawn a picture to explain the connections and am including a link.

        Please can you provide your expert advice once again.

    • ibraheem September 17, 2014 at 18:15 #

      hi, i have ur exact issue, dc wires to my thermostat pls let me know if u had ur nest working thx

  8. Martin September 6, 2013 at 09:57 #

    Hi, can you ship me the RC840-240 in Slovakia?
    I would buy it. I have this heating system – http://store.heatflow.co.nz/en/ and i want to control with the nest termostat…

    thank you

    • usingnestineurope September 6, 2013 at 10:35 #

      Yes i could if you are sure 100% this is the device you need (rc840)

      • Martin September 6, 2013 at 11:41 #

        How much is the postage and how will I pay?

  9. Stephen September 8, 2013 at 20:48 #

    Hi Matt

    Really useful site.

    I am in United Kingdom
    I have Nest but have not set it up yet.

    The RC840 looks really great..

    Would you still have any left to sell and sent to me?

    Thanks Stephen

    • usingnestineurope September 8, 2013 at 20:49 #

      Yes i do actually
      What is your heating system made of?
      What is your thermostat like currently?


      • Stephen September 9, 2013 at 18:14 #

        Hi Matthieu

        I have an “Ideal” gas boiler with a 240v two wire standard Honeywell Thermostat.



      • Stephen September 10, 2013 at 18:10 #

        Hi Matthieu

        Could we exchange contact details and arrange a price for one of your RC840’s to post to England.



      • usingnestineurope November 8, 2013 at 22:54 #


        Are yous till looking for a rc840?
        Did you get your nest to work?
        I believe i am in a position to sell you one and can investigate shipping costs


      • Stephen November 9, 2013 at 12:04 #

        Yes I am still interested in RC840
        I have not set up my Nest yet.
        Could you deliver to Stockport England..


      • usingnestineurope November 9, 2013 at 15:24 #

        Will do and keep you posted…


  10. Matteo September 9, 2013 at 17:00 #

    Hi, I’m Matteo from Italy.
    My Aube RC840T has just arrived from Canada and I’m installing my Nest 2.0… But I too have a bad headache for the wires.
    The old thermostat is a Honewell T6661B with only two wires attached, the A and the B. See the picture:

    I’ve tried many combinations, but still no luck, any guess?

    • Matteo September 9, 2013 at 17:10 #

      The three wires of the RC840: C, W, R go into the Nest in the order C, W1, Rh.
      The problem are the three remaining wires, the Black, the Blue, and the Red.
      I’ve tried to connect the Red with A, Black with B, and Blue with the neutral I took from a near plug. Also Blue -> A, Black -> Neut, Red ->B nothing…

      • usingnestineurope September 9, 2013 at 19:45 #

        It seems you should try black with A,
        Red with B,
        Blue with your neutral,

        But this is lethal voltage so i assume no responsabilities,
        You needa voltmeter,


  11. Matteo September 10, 2013 at 13:34 #

    Hi, I couldn’t manage to find out what was wrong until I tested with a voltmeter. Result: the two wires A and B are low voltage, 24v, so they’re ready to be connected to the Nest. So I plugged the A -> W1 and B -> Rh… The Nest recognized them but tells W1 has no power, but it let me go further and save. The problem is that the furnace is always on, as it never disconnects the A B connection.
    Reading in the help seems correlated to the charging of the Nest, so they suggest to wire the C cable… Here I am a bit confused because if I use an external transformer for the 220v -> 24v I’ll have two wires, the positive and the negative one. One goes to the Nest C slot, but the other one?

    Thanks for you reply!

    • usingnestineurope September 10, 2013 at 17:24 #


      this all sound scary… I assumed you had ad-hoc test equipment.

      what brand and model is your heating system?
      do you understand who your heating system was working with your Honeywell thermostat?


  12. Matteo September 10, 2013 at 17:43 #

    The heating system is a Sime model Murelle EV. I have changed it last year, but they left the old thermostat which is a Honewell T6661B. It all works with 2 cables, they are 27V, if they are shorcircuited, the heating systems starts heating the radiators. This is what the Nest expects, wiring the W1 and the Rh.
    If I connect the cables to the nest they starts the heating, regardless of the nest control, even if off.
    I’m looking if the problem is the nest that needs charging and uses the two cables. So I bought a 24v transformer to add the C cable, that is supposed to charge the nest, leaving it from taking power from W1 and Rh, as in this video: http://www.youtube.com/watch?v=BgDseEF-4OY

  13. JM October 26, 2013 at 16:49 #

    I have a Nest 2.0 and the Aube RCT840T that I am trying to connect to a Vaillant Ecotec Plus 937 (in the UK).
    I initially tried to connect it to the 24V Room thermostat connectors on the boiler, but it didn’t provide sufficient power to charge the Nest.
    I decided to go for the RCT840T solution. However the Vaillant boiler can only accept two 240V wires for the 240v room thermostat.
    How should I connect the Aube really to my boiler?
    Here is a link to the Vaillant connection diagrams:
    Any help is appreciated,
    Thanks in advance,

  14. JM October 26, 2013 at 16:51 #

    Just to specify, the 240V room thermostat connectors are located in the X1 section just above the main connection.

    • usingnestineurope October 26, 2013 at 20:31 #

      Good day JM

      I only see one wire dedicated to your 230v thermostat, i could be wrong…

      Can you confirm by default how many wires go to your thermostat and where are they precisely departing from your x1 connector please?

      • JM October 26, 2013 at 23:43 #

        Thanks for your quick reply.
        By default, I have two wires going to my thermostat and they depart from two top RT connectors on the X1 section (where it says no function and 230V Ac room thermostat).
        Basically, both the 24V and the 230V room thermostat connectors are simple on/off circuits that the thermostat controls.

      • usingnestineurope October 26, 2013 at 23:48 #

        Ok so i guess when your thermostat calls for heat (at least the 230v one) dors short the two Rt wires on your X1 connector, is this correct?

        A follow up question i have:

        Is your thermostat far from your boiler?
        Do you have 3 wires by any chance available in the wall behind your thermostat?

  15. JM October 27, 2013 at 12:54 #

    It’s a completely new installation, we have replaced everything: boiler, plumbing and thermostat wiring. I installed 6 wires for the thermostat, just in case as I won’t be able to replace it in the future. Also, I knew that the Nest would require at least 3 wires.
    So far, only two have been used.
    The thermostat (ground floor) is quite far from my boiler (second floor).

    • usingnestineurope October 27, 2013 at 15:32 #

      this is perfect, you are a wise man having reserved 6 wires. I will customized one of my previous drawing and make a recommendation for you – it looks simple…but as usual, please use caution, 220-230V can be lethal!

      • JM October 29, 2013 at 21:35 #

        Thanks again for your help.

  16. Feridoun November 3, 2013 at 13:18 #

    Hi everyone, just wanted to share that I got my Nest thermostat working with a 24v transformer and 24vac relay using the following wiring. My boiler is a Vaillant Ecotect plus 837. http://imgur.com/JjHJQq2 .

  17. Vincent November 7, 2013 at 11:29 #

    Salut Matthieu,

    J’habite ds les Yvelines du côté de St Germain en Laye et me demandait si tu pouvais m’aider pour installer un Nest ds notre maison.
    La chaudière (murale gaz Frisquet) est très récente apparemment (- de 2 ans) et fonctionne avec un thermostat radio si j’ai bien compris…



    • usingnestineurope November 8, 2013 at 22:52 #

      Bonjour Vincent,

      J ai tres peu de temps libre, as tu un nest en ta possession et un rc840?
      Sinon j ai de quoi te depanner


  18. Ty Stewart November 14, 2013 at 21:30 #

    Hey Matt… question for you. We recently moved to Belgium from the US. We are in a fairly new home here with Radiant Heat (heat only, no cooling). We have a Bulex Thermomax F24 – Natural Gas. It’s connected to a very simple Danfoss RMT 230 2 wire (blue & black) Thermostat – although there are 3 other wires (brown, grey, yellow/green) not connected coming out of the wall. First off, is it even possible to get a NEST to work properly? Second, what would i need? Appreciate the help!

    • usingnestineurope November 14, 2013 at 21:50 #

      Hi welcome to Europeand the world of 220 volts!

      It seems possible the main challenge currently is to bring the power supply to the Nest

      I would need to investigate what your boiler is like etc…


  19. Amit Adalja November 16, 2013 at 06:11 #

    Hi could you please send me schematic & tutorial, i shall be using Nest thermostat for my home air-conditioner.

  20. Ajit December 3, 2013 at 19:18 #

    Hi Mathieu
    I was wondering if one could use aube rs840-240t relay for cooling(home air conditioning ) with the Nest thermostats.


    • usingnestineurope December 3, 2013 at 21:50 #

      Sure no problem

  21. Piyush January 7, 2014 at 16:05 #


    Would be extremely grateful if anyone can help me with below:

    I want to replace my Daikin Thermostats with a Nest Gen 2 thermostats. (I have Daikin Split Ducted Air conditioners only – NO Heating)

    However my Daikin Thermostats are 5V DC.

    Details and pics as follows:

    Yellow: Signal wire
    Black: Ground
    Red: +5V DC
    White: Signal wire


    From what I understand, the Yellow wire and White wires will connect to the NEST Y1 (compressor) and G (Fan). However the Red wire is a 5V DC current whereas NEST Rh connection accepts 24V AC current.

    1) Request pls advise whether the Red 5V DC wire can be connected to the Nest RH connector (which is 24V AC as far as i understand) ?
    If Not, pls advise is there is any work around ?

    2) Alternatively Can I ignore/Remove the red wire (+5V DC) coming from my Indoor Unit and use an EXTERNAL 24V AC power adapter as Power source to the NEST ?

    “IF this is a possible solution – then the External 24V AC Power adapter has “2 wires”. Can I connect only one of the wires to RH on NEST ? -OR- Should I connect one of the External 24V AC Power adapter Wires to RH on NEST and the 2nd wire to “C” (Common) on the NEST ?

    Any help on above will be highly appreciated. Thanks.


  22. Jeroen January 17, 2014 at 17:20 #

    Hey MB,

    I installed the same setup but unfortunately the thermostat wont stop heating for some unknown reason. Is your setup also 50 Hz ?

    Thanks to whoever knows the answer 🙂

    • usingnestineurope January 17, 2014 at 18:14 #

      yes it is 50 Hz as well… I am trying to think why is your Nest heating all the time…

  23. Jeroen January 17, 2014 at 20:49 #

    From what I have now I can only think that there is something wrong with the base plate. I’ve tested each possible scenario (turn down thermostat, turn up, turn of, reset thermostat, disconnected the display) and heating stays on the whole time.

    You should think that whenever you disconnect the display the heating stops but nope… still pretty hot in the living room. (LED on the relay is lid up)

    The only way to stop heating is disconnect the W connector.
    if it could be in your interest, I’ve attached a little image.


    • Jeroen January 18, 2014 at 17:40 #

      Hey MB,
      Nest support told me I have a blown FET on the base. They will send me a new one.
      Thanks anyway for the response and also your blog. Helped me a lot!

      • usingnestineurope January 19, 2014 at 21:10 #


        I am pleased you got some support from Nest with this setup and despite nest not having officially launched in mainland Europe.

        On my side i am working on assessing the savings achieved with Nest…

        Will be posting results once i have something meaningful


  24. Abdo February 10, 2014 at 10:21 #

    Dear sir,

    Iam planning to install the nest here but I found that we use 220v .

    I have attached two photos of thermostat wiring using now and working here for air conditioning . so you think rc840 will be solving the issue ?

    And if so how would I be able to connect my wires to rc840? And will it work for air conditioning ?


    • usingnestineurope February 10, 2014 at 14:50 #

      Yes nest can work with 220v control signals using caution

      • usingnestineurope February 10, 2014 at 14:58 #

        You seem to have a have a dry contact required on your “valve” side, plus you have both line and neutral available for the 220v supply

  25. Funyo March 14, 2014 at 18:22 #

    Hi, I have just discovered your blog page… I have just bought two Relays RC840T – 240V and when I opened the box I found Relay on which is written 60Hz only.. On the box it says 50/60Hz. I want to use it with my Nest Thermostat to control circulating hot water pump of my under floor heating in the Czech Republic. Do you think it will be a problem to operate this 60Hz Relay on 220V/50Hz?? Thanks for any advice …

  26. Funyo March 14, 2014 at 19:24 #

    Follow up to my previous post. This is an official respone I got today from one of the Canadian RC840T – 240 V re-sellers, AARtech Canada: “Aube technical support just came back and said the product is only for 60 Hz for North America. It used to be 50 Hz but not for several years apparently but they had not updated their web site to indicate the change. We are addressing that with Honeywell…”.

    … however, I still believe it will work on 50Hz just fine and do not overheat!
    Any experience with the Relay?

  27. usingnestineurope March 14, 2014 at 20:49 #


    Thank you for your post,
    No issues to be reported with aube on 220v 50hz here in France with nest thermostat only use in heating and with a natural gas heating system.
    As a side comment, the aube rc840 was not switching high current. Rather it is was switching about 80 to 100 mA at 220v.

    Concerns may exist should you be switching tens of amps at 220v and 50hz….

  28. Funyo March 14, 2014 at 21:15 #

    Since our Relay RC840T – 240 comes with Built in 24V Transformer I found this artical on the web very interesting: “A transformer rated for 50Hz can be used anywhere in the world – it will work perfectly at 60Hz. However, the converse is not true. A transformer designed specifically for 60Hz will overheat at 50Hz, even if the voltage is correct! This is not well understood, and leads to an enormous amount of traffic on Usenet and in forum pages everywhere. The answer is quite simple – 60Hz is 20% greater than 50Hz, so the core and turns per volt can both be reduced by up to 20% compared to a 50Hz transformer of the same rating.

    Therefore, a transformer that was designed for 60Hz at 220/230V (The Philippines, South Korea and a few others use this combination [Ref]) has a smaller core and fewer turns than an otherwise identically rated 50Hz transformer. As a result, it will most likely fail with 220V at 50Hz. Operating a 60Hz power transformer at 50Hz is exactly the same as operating the transformer at its rated frequency, but with a 20% voltage increase. If you absolutely must run a 60Hz transformer at 50Hz, you must reduce the mains voltage from the rated value (say 230V) by 20% (184V). This is a large drop, and exceeds the normal mains variation allowances that are provided for in properly designed circuits.

    Failure to reduce the voltage will cause the transformer to be heavily into saturation, and it may easily consume half its rated VA (or more) at idle, due to excessive magnetising current caused by core saturation. Needless to say, the secondary voltage will also be reduced by the same percentage. For evidence of the current increase due to core saturation, see the next section (specifically Figure 12.1.1).

    Operating a 60Hz transformer at 50Hz is effectively the same as a 20% increase in mains voltage, but note that this does not mean that the secondary voltage is increased. For a 230V transformer that’s the same as running at 60Hz, but at a supply voltage of 276V. The core will be seriously saturated, and the magnetising current will be increased dramatically.

    Should the power transformer be for a valve amplifier, care is needed, because the valve heaters will be operating from a lower than normal voltage (6.3V will only be 5V) and may not reach the proper operating temperature. Output power is also reduced, and a 20% reduction of voltage will reduce the maximum power to fall from (say) 100W to 64W, a drop of just under 2dB. It also means that all unregulated preamp supplies will be 20% lower. With regulated supplies, the drop might be enough to cause the regulator ICs to allow rectified mains buzz through to the signal circuits.

    For information about how you can reduce the supply voltage (in this case by 46V), see the article Bucking Transformers. While the methods described certainly do work, the other compromises you have to make will almost certainly mean that the transformer will have to be replaced to maintain original performance.

    Should you have a transformer rated for 240V at 50Hz and wish to use it at a lower voltage and/or 60Hz, then there is no problem. If used at 120V 60Hz, the transformer will operate with an exceptionally low magnetising current, but the secondary voltages will obviously be halved. While the maximum current rating remains the same, regulation will be worse than a transformer wound for 120V mains because the winding resistance is higher.

    In short, you can operate a …

    50Hz transformer at 60Hz with no loss of performance, provided voltage is correct
    50Hz transformer at 60Hz at a supply voltage up to 20% higher than the nameplate rating
    transformer at any voltage below the nameplate rating. There is no limit other than that imposed by common sense
    60Hz transformer at 50Hz, provided the supply voltage is 20% lower than the rated voltage
    Likewise, you cannot operate a …

    60Hz transformer at 50Hz at full rated voltage
    transformer at any voltage above the nameplate rating, unless rigorous testing shows that it will be safe (unlikely)
    Note that I have simply assumed 20% in both directions (50Hz to 60Hz and 60Hz to 50Hz), although it is clear that a reduction from 60Hz to 50Hz is actually 17%. Feel free to think of the extra 3% as a safety margin”


    • usingnestineurope March 14, 2014 at 21:25 #

      Excellent info, thank you for sharing this!

      Seems like a schematic is in order for those who want to experiment the buck transformer approach… Not dure i have the bandwidth to do this

    • Funyo March 14, 2014 at 21:30 #

      Anyway, I am going to install my first Nest Thermostat next week in the Czech Republic which will regulate circulating pump in the manifold of our undefloor heating system and I will see if that will work or not…
      I have no problem to supply 24V to Nest, my concern is whether my 60Hz Relay continuously operated on 220V/50Hz by sending signal for heat on/off, will overheat or cause any other problems..
      Anyone interested, stay tuned and I will provide some feedback soon…

      • Funyo March 23, 2014 at 22:03 #

        Okay, there is my feedback, I ihave just nstalled my first Nest Thermostat with the RC840T-240 Relay on my 220V/50Hz current and .. It all works just perfect… the 60Hz Relay does not everheat and it works great when calling for heat — switching on/off my circulating pump of our in-floor heating system! Can recommend! 🙂

      • usingnestineurope March 23, 2014 at 22:53 #

        Excellent news Funyo,

        For everyone’s benefit would you
        Please confirm the brand name and model of the heating system used at home?

        What country are you in?


  29. Makk1000 March 25, 2014 at 23:37 #

    I live in the UK and I have recently installed the Nest v2 thermostat with a Glow Worm 24ci Gas boiler (no previous thermostat). It was actually very simple as the boiler has 24v connections on it (2 wire). I pre-charged the battery on the nest, then wired it to the W1 and Rh connections. That was it! It powered up!
    I only ran into a few issues so far… first it will display on the device that W1 has no power. This is probably because the 24v connections are for ‘dumb’ analogue thermostat but it is drawing power through Rh which is important as it use this to keep battery topped up.

    Second, I initially found it would only momentarily turn off boiler once room reached chosen temperature… this I found out was related to ‘W1 no power problem’ just not enough juice from the nest to trip the switch. I got around this by using the boilers analogue timer to do it! I just switched the timer on, set the timers dial switches to be on 24hours a day and presto the signal from the nest is now strong enough to turn the boiler on and off!

    I will report back in a week or so to inform if the battery keeps it charge on this set up but it has been three days so far and all seems well.


  30. Thomas October 26, 2016 at 21:47 #

    I have a gas heater / furnace controlled by a simple elv4c I am replacing this with a nest and rc840T there are only two wires coming from my breakout box and con eating to the elv4c wich wires should I connect to the rc840t ?

  31. Simon Smithson January 18, 2017 at 19:25 #

    Hi all,

    I currently have a Siemens RAA20 thermostat that I’m looking to replace with a Nest. I’ve bought an RC840T but I’m a little confused how it should be wired.

    My thermostat has 2 wires connected currently, marked L and Y1. There’s a 3rd unconnected wire in the wall. Between the unconnected wire and either of the connected wires there is 240v. Which leads me to believe that the unconnected wire is neutral and that the thermostat is effectively a on off switch on the live wire.

    So though I seem to have all the important info, I can’t work out which wires go where on the RC840T.

    Can anybody help please?

    p.s. The Nest is a 2nd gen model without heatlink.
    p.p.s I’m in the UK.

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