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Tuya smart thermostat - combi gas boiler

Discussion in 'Plumbing and Central Heating' started by Rob3982, 18 Feb 2021.

  1. Rob3982

    Rob3982

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    Hi all,

    I'm trying to replace my Honeywell digital thermostat for a WiFi Tuya thermostat.
    I think I've got it figured out but I want to run it past someone.
    This is my current wiring,
    IMG_20210218_151941.jpg
    And the back of my new thermostat,
    IMG_20210218_152747.jpg

    I plan to put Brown into 4, Blue into 3 and Black into 2.
    Is that right?

    Thanks.
     
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  3. stem

    stem

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    Your existing thermostat is battery powered and the wires in A & B are the switching wires. With combi boilers there are two possibilities. They can be wired for 230V control or 24v control. The new thermostat you have will only work with 230V control. So first of all you need to determine which way your boiler is connected. It does appear from the presence of a brown sleeve over the black wire that it is 230V, but this cannot be taken for granted it should be checked with a multimeter. If it is 24v you cannot connect it to the new thermostat.

    If it is found to be 230V, the two wires in A & B will be a 'live' and a 'switched 'live'. Being battery operated there is no need for a neutral connection at the existing thermostat. The blue wire at the back may be connected to a neutral at the other end, or it may also be left unconnected at the other end, so this too needs testing to find out.

    The next problem you have is determining which of the wires in the existing thermostat is the live, the diagram shows the L terminal as A, but the brown wire which is normally used as the live is in terminal B. Testing the wires will identify the live supply wire and which wire is switched 'on' and 'off' by the thermostat. [A battery thermostat will work with them connected either way around]

    Once you have identified the wires then:

    Neutral goes to [3] N
    Live goes to [4] L
    Switched live goes to [2] Open
     
    Last edited: 18 Feb 2021
  4. Rob3982

    Rob3982

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    Thanks for replying so quickly.
    So I've got the wiring correct, but I need to confirm a few bits first.
    I've got a multimeter so I'll test the voltage. I assumed it would be 230v.
    How do I test the neutral, live and switched?
     
  5. stem

    stem

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    With a multimeter on a known neutral or earth, such as on the fixing screw in a nearby socket. You can test for a live on Brown or Black. The one that is still live with the cover off the thermostat as in your photo is the live. [if there's a programmer or timeswitch somewhere that will need to be set to heating 'on'] Once you have determined the live, you can then use that as a reference with the unconnected blue wire. 230V between the two will confirm it is a neutral
     
  6. Rob3982

    Rob3982

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    Brilliant, thank you.
    That'll be my Friday!
    I've found the boiler manual. It suggests the live is connected to the switch (diagram C), but the back of the new stat suggests the neutral is. Could this be why the brown and black appear to be reversed?
    16136749388381273886228456376973.jpg
     
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  8. Rob3982

    Rob3982

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    Brilliant, thank you.
    That'll be my Friday!
    I've found the boiler manual. It is 230v
    It suggests the live is connected to the switch (diagram C), but the back of the new stat suggests the neutral is. Could this be why the brown and black appear to be reversed?
    View attachment 223532
     
  9. Rob3982

    Rob3982

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    I didn't mean to post twice. I got an error message.
     
  10. Rob3982

    Rob3982

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    Now I'm on my laptop I can see my pictures a lot clearer.
    The black wire has a brown sleeve, so that's my live.
    I'll test the neutral tomorrow and wire it up.
     
  11. stem

    stem

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    There's more than one way to skin a cat. It could be connected as per diagram A

    Both wires connected to the existing thermostat terminals A & B are live wires. You need to find out from your test which one is the supply live.
     
  12. Rob3982

    Rob3982

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    All wires identified and it's gone in seamlessly.
    IMG_20210219_123052.jpg
     
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