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Is it possible to swap a dial Honeywell T630 thermostat with a NEST thermostat?

Discussion in 'Plumbing and Central Heating' started by Smileysmile, 13 Dec 2019.

  1. Smileysmile

    Smileysmile

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    My house was built in 2001 and it has the dial thermostat T630. I want to change it for a NEST digital thermostat where I can alter the temperature from my phone etc
    I read somewhere if it 120v or 230/40 volts you can't replace with a NEST.
    Does anybody know if this is true? Thanks
     
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  3. Chris_W

    Chris_W

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    Which nest?
     
  4. stem

    stem

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    The Nest Heat link part requires 230V mains supply to power it connecting to N and L on the left.

    The Nest thermostat requires 12v to power it this can come from a USB adaptor, or by wiring it to special 12v terminals inside the Heat link. (T1 & T2) on the right

    The actual switching contacts (Terminals 1 to 6) are voltage free, so can switch whatever voltage is applied to them 230V and 24v are the most common, which may vary depending upon your system. Some systems the thermostat is wired to the boiler and the boiler provides the control voltage (eg 230V or 24). Other systems have motorised valves which are 230V.

    Capture.JPG
     
    Last edited: 13 Dec 2019
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  5. Smileysmile

    Smileysmile

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  6. Smileysmile

    Smileysmile

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    Stem you have completely bamboozled me. I was looking for a straight swap.

    My current dial Honeywell thermostat has 4 wires. I think it 230v and this video clip tells me it won't be compatible. So I need an adapter? Where would I put that? Thanks
     
  7. stem

    stem

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    That video is of a USA Nest that us used with their furnaces. It cannot be used in the UK. They work completely differently to our systems and their voltage is different to ours.

    There are two sorts of Nest you can use here, the most common is the 3rd Gen that has a separate thermostat and Heat link that I gave details off, and as in the screwfix link you posted. The other version suitable for the UK is a battery operated e-Nest, but this doesn't provide hot water control.

    Also to be considered is the type of heating system you are planing to use the Nest with. If it is a combi boiler without a hot water cylinder connected to it, or a system that has a programmer controlling hot water and central heating. The installation method will vary.
     
    Last edited: 13 Dec 2019
  8. Smileysmile

    Smileysmile

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    Stem
    I have the latter, hot water cylinder. Are you able to point me in the right direction with a NEST like the one I posted? A straight swap? I can turn off the mains and swap both by myself.
     
  9. Chris_W

    Chris_W

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    You should be ok with the one you posted, but it’s the programmer wiring that will be different, as your Honeywell just controls the heating for the room. Your programmer will be another on/off switch.
     
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  11. stem

    stem

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    Then you need the Nest Gen 3 as per the screwfix link. But it's not a straight swap exactly. The Nest Heat link will replace your existing programmer.

    1.jpg

    Because this is where the heating and hot water system wiring is, and the wires can be moved from the existing programmer to the Heat link. Then the old room thermostat should be removed and a slight wiring modification made to bridge its removal

    The Nest thermostat

    2.jpg

    Then communicates wirelessly with the Heat link. The thermostat can be powered via a plug in power supply or connected to the Heat link, whichever is easier.

    If you post details of your existing programmer and room thermostat a more definitive answer can be given.
     
    Last edited: 13 Dec 2019
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  12. Smileysmile

    Smileysmile

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  13. ianmcd

    ianmcd

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    Did you expect a magic potion to sort it ?
     
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  14. stem

    stem

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    If you don't understand what I have posted, you would probably best advised to get professional installation.
     
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  15. Smileysmile

    Smileysmile

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    Stem
    So what you're saying is I have to replace my current central heating/hot water programmer to be able to communicate with a NEST thermostat? Which is fixed to my tiled kitchen wall under boiler in my kitchen?
     
  16. Chris_W

    Chris_W

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    If you want the Nest to control hot water as well yes, if you just want a room thermostat then no. The new ones include hot water control so don't know if it would work, in which case you may be better with https://www.screwfix.com/p/google-nest-smart-thermostat-e-white/199fj
     
  17. stem

    stem

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    That's the idea.

    The Heat link
    [​IMG]
    Contains two simple switches inside, one for the central heating and one for the hot water.

    The programmer, hopefully something similar to this...

    1.jpg

    .....also contains two simple switches inside for the central heating and hot water, exactly the same. So, the programmer is removed and the wires removed from its terminals go to the terminals of the Heat link that have exactly the same function. No additional wires will be required, only what is already there will be needed. [Assuming your existing system is wired and working correctly]

    If you don't want to have the Heat link where the programmer is, it can be located somewhere else, but it then becomes quite a major wiring job, not just a simple exchange of one item for another.

    The old existing room thermostat needs to be decommissioned to stop it interfering with the Nest. This is done by tracing the existing thermostat cable back to its origin, disconnecting it and then inserting a wire to bridge the terminals where the two live wires that went to the thermostat have just been disconnected from. [If that's too difficult, the old thermostat can be left where it is and set to its maximum setting]

    Finally the Nest thermostat requires 12v to power it. It can get this by being wired to the Heat link, (terminals T1 & T2 are provided specifically for this purpose) or by using a separate plug in power supply for it.
     
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