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Combi Boiler to Nest , Please help!

Discussion in 'Electrics UK' started by AngelaBrady, 23 Dec 2020.

  1. AngelaBrady

    AngelaBrady

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    Hi all,
    Hope you are all well.
    Am trying to install a nest 3 gen in my flat with a combi boiler.
    I have a Honeywell timer ST6100A with a frost room thermostat and a combiner's boiler 24i green star junior. The timer controls hot water and the room thermostat controls central heating. I need help wiring nest heatsink instead of timer and nest thermostat instead of room thermostat please! There is a spur of a 3amp fuse.

    Here is the timer:
    Here is its wiring:
    Here is the thermostat:

    Please advise as my bf s away and I have no clue what this all means.
     
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  3. ericmark

    ericmark

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    On the timer N L 1 and 4 will go to N L 2 and 3 the N and L must go to right place. 1 should got to 2, and 4 should go to 3.

    However some where behind the timer there will likely be some connectors where the cable to thermostat is connected, and the problem is going to be working out which those wires are and since with Nest Gen 3 those wires will be 12 volt and with original likely 24 or 230 volt clearly you can't afford to make a mistake, I used a multi-meter to check my cables were not connected to 230 volt before reusing them to carry 12 volt from heat link to Nest thermostat.

    I think the boiler you have is Bosch and I don't think Bosch have signed up to Opentherm so you only have option of on/off control with Nest, it was same with my Bosch boiler, however I would not be happy reusing cables without using a meter to ensure I had the right ones.
     
  4. AndyPRK

    AndyPRK

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    I'd leave it alone until after Xmas. You don't want to be without heating over xmas
     
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  5. Chris_W

    Chris_W

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    1st and foremost, safely isolate and confirm.

    L Honeywell to L Nest
    N Honeywell to N Nest
    1 Honeywell to 2 Nest
    4 Honeywell to 3 Nest

    Disconnect the thermostat wires from connections at timer, and use these 2 wires going to T1 and T2 - Doesn’t matter which way around, there’s no polarity. Remove wires at thermostat, and install Nest backplate and fit wires to T1 and T2 terminals. Since the earth is there, I think you need to connect this both ends of Nest as well.
     
  6. sparxxxx

    sparxxxx

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    I would leave until after christmas.

    You also need to decide whether you want your existing timer and stat completely removed, this means the nest packs up you have no heating. Or piggy back the nest on top of existing timer and stat, this means if nest packs up you can revert back to stone age controls
     
    Last edited: 23 Dec 2020
  7. ericmark

    ericmark

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    I would agree, I would not play with heating in Winter, you install new systems in the Summer so any problems then time to correct.

    At moment without a car, was simple problem, hole in side wall of tyre, but can't get replacement, I can do without a car, but doing without central heating is not so easy.
     
  8. AngelaBrady

    AngelaBrady

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    Hi guys! thanks soooooo much for your help.
    I totally agree that I should not attempt anything in these cold days! I just wanted to know that I can actually fit a nest. If all good i am willing to buy one during January sale to install in summer.
    My boiler is wocester 24i greenstar junior. Is it compatible for nest to control both heat and water when i remove my old timer and room thermostat?
    Thanks
     
  9. Chris_W

    Chris_W

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    Hot water is irrelevant, it’s a Combi boiler - hot water on demand.
     
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  11. ericmark

    ericmark

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    As far as I am aware the Worcester Bosch boilers have never adopted opentherm they have with some models an ebus control option, however this means control is one area only. So in the main Worcester Bosch boilers have a simple on/off control for the electric side, all the real control is done on the water side by monitoring the return water temperature, so nearly any wall thermostat will work, even ones like Nest with opentherm still have the on/off option.

    So the big question is will one thermostat with no link to TRV heads do what you want? I fitted Nest Gen 3 as I wanted hard wired install and Nest allowed this with my system, and at the time of install I thought Nest would work with the Energenie MiHome TRV heads I already had, however it seems Nest has withdrawn support.

    I will admit the Nest geofencing seems to work well, but the learning feature does not seem to learn what the programmable TRV heads are programmed to do, not that we can really expect it to, so you have to consider what is the best control for your way of life and your house, if your going to install Nest then stop, likely Nest will work well, but if you want to add programmable TRV heads, then the first job is look at what programmable TRV head you want to go for.

    So super cheap eQ-3 at £10 does not connect to any wall thermostat so does not matter which you have, same with Terrier i30.
    Then there is a big jump in price, the Energenie MiHome I have seem to work the wrong way around, the wall thermostat controls the TRV if linked and the whole idea is not to have every room at same temperature.
    The rest the TRV tells the wall thermostat what to do, EvoHome has a nice central hub from where you can control all, Drayton have Smart TRV's that work out time to heat a room, Hive is another odd one, the TRV sends a demand for heat to the wall thermostat which turns the wall thermostat on for ½ hour.

    However you need to consider what in fullness of time is your aim, and select the product which will not only do what you want now, but also will still do what you want in 5 years time. I admit it does not always work, I selected Energenie MiHome TRV heads with the idea of adding Nest latter, and when I got Nest found support had been dropped. I also told loads not to buy Hive as it was not really "Smart" and did not work with TRV heads, then they released a range of heads, so now still not really "Smart" but it does do a lot more than it did.

    Reading reviews it seems Hive has had problems with the wireless linking, and have released a more powerful hub, but as to if because some houses use a insulating plaster board which turns the rooms into Faraday cages, or if original not powerful enough I don't know.

    It seems no good asking heating guys, as they don't live in the houses, so they don't know how well each geofencing works, or how good the algorithms are, we just stick in a pin. And in the main owners do not want to admit when they get it wrong. And even when they do, never sure if really something wrong or some thing they did.

    In Mothers house with Worcester Bosch combi gas boiler the Energenie MiHome TRV heads after a few teething problems worked well, this house with Worcester Bosch oil system boiler they have not worked as well, however since we took them with us from last house, we have never tried to live in this house with non programmable TRV heads. So could be house design.
     
  12. AngelaBrady

    AngelaBrady

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    thanks to all of you but i m a bit slow when it comes to electricity. if i hire an electrician to install it.
    1- hive or nest is better in my case?
    2- do i need to call the elctrician for maintenance or it s one off?
    3-I f there is no internet or it is slow. so no heating nor hot water
    sorry and please bear with me
    much appreciated
    Merry Christmas
     
  13. Chris_W

    Chris_W

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    I think they work without internet, just losss all singing all dancing bells and whistles. Hive/Nest is preference, no maintenance fees, just one off.
     
  14. AngelaBrady

    AngelaBrady

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    Hi, do T1 and T2 have to have 12V ? I tried to measure using a multimeter but couldn't get an accurate reading.Also do I need 12V at the thermostat ?
     
  15. Chris_W

    Chris_W

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    Hi, I didn’t mention voltage. The 12v is delivered by the heatlink to the existing thermostat, on the existing wires. You don’t need to measure it. Yes it has to have the 12v, but as I said this is delivered by the heatlink output.
     
    Last edited: 6 Jan 2021
  16. AngelaBrady

    AngelaBrady

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    Hi Chris,
    somebody mentioned that if T1 T2 didn't have a supply of 12 V then it would blow the nest?
    My trouble is identifying which wires are T1 and T2.

    When I removed the box I found another set of wires, fine wires, in a junction together one grey and one brown.
     
  17. Chris_W

    Chris_W

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    Hi Angela,

    Just gone over the post and Eric said make sure you don’t connect 230vac to the 12v side. The T1 and T2 are the brown and blue at your existing thermostat end (hence Eric’s comment). You need to remove the existing thermostat, Brown, blue and green/yellow, and connect them to the nest thermostat base plate then at your timer end, you have brown and blue which are common and call for heat, and the thermostat is connected somewhere.
     
    Last edited: 6 Jan 2021
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