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Discuss Replace Heatmiser with a Nest in the Central Heating Forum area at

  1. david007

    david007 New Member

    hi I’m thinking of changing my thermostat ( Heatmisertouch screen programmable) to a Nest. I currently have an old WB 28cdi RSI and will be replacing it with a Vokera 38kw Combi. Am I right to assume that all the wiring from the new or old boiler goes starlight to the heat link thing ( including power) and the only 2 wires from the heat link to the boiler are the low T1 & T2( low volt). It’s an opentherm boiler. It’s rather challenging! I’ve put a pick up of the current stat wiring.


    • Optimistic Optimistic x 1
  2. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    I would keep the heatmiser maybe update it if it's the old one
  3. Ric2013

    Ric2013 Plumber

    No idea, I'm afraid.
    But thanks for the pic of the thermostat. Yet another installer who has never heard of a backbox lol.
  4. scott_d

    scott_d Plumber GSR Top Contributor!!

    Doesn't sound right to me.
    • Like Like x 1
  5. david007

    david007 New Member

    Each to his own, I could elaborate at how ept I am about using a life support machine in intensive care units and that I have a Doctrare. This site is for DIYers as well. It was a simple request for some general info LOL. However I’ll bow my head to your superior intellect in your own particular field.
  6. david007

    david007 New Member

    It is. I just needed the external temp and Nest was easier. Thank you
  7. Chalked

    Chalked Plumber GSR

    He wasn’t meaning you! He was referring to the installer.
    Back to your post , keep the Heatmiser, as nest is,a glorified data gathering device.
  8. david007

    david007 New Member

    My apologies to all.
    • Like Like x 1
  9. Ric2013

    Ric2013 Plumber

    I could easily throw that sarcasm back on you, but I'll bite my tongue ;)

    My point was that I was being sympathetic that, like myself, you've bought a house that comes with electrical installations that are clearly in breach of electrical regulations. It happens often, sadly. And often that sort of mistake is made by people who really ought to know better, i.e. tradesmen!

    I can't comment on your original question because I do not have the relevant knowledge, hence saying 'no idea'.

    Had I thought that you'd wired that yourself, my comment would have been to the effect that exposed cable cores outside of an enclosure are illegal and dangerous, and so, while you're about it, get a backbox to fit behind whatever you replace that thermostat with and make a real improvement.

    Better still, if you are going to do DIY electrics and you do not know that cable cores need to be in a cable sheath or enclosure everywhere, then you really need to get a good textbook on the subject and read it cover to cover before you start. You just won't always get the level of instruction you need from websites. This textbook is quite a good one, I think:
    The Electrician's Guide to the 17th Edition of the Iet Wiring Regulations BS 7671: 2008 Incorporating Amendment 3: 2015 and Part P of the Building Regulations
  10. david007

    david007 New Member

    Thank you for your time. Duly noted. There was no intention to offend. There was beer anyintention to offended. Apologies again.
  11. scott_d

    scott_d Plumber GSR Top Contributor!!

    Might be best to get the new controls fitted when the boiler goes in
  12. AMGasServices

    AMGasServices GSR

    It is pretty simple when using the opentherm. I’m pretty sure it will be a wireless connection.

    No need to disturb the existing thermostat. Do all the change over with the new boiler installation.

    The difficult part is setting and pairing it all up.
    • Like Like x 1
  13. david007

    david007 New Member

  14. sparkie30

    sparkie30 Member

    Hello David,

    Im afraid you are not correct.

    T1 and T2 are used to supply the thermosatat from the reciver, thermostat requires a 12v dc to operate but the switching is between stat and reciever is carried wirelessly.

    For a combi boiler you woud a 2nd gen nest stat, a 3rd gen would work aswell but it is designed for boilers with cylinders.

    See diagram how you would wire a combi boiler.


  15. david007

    david007 New Member

    Thanks mate

    I’m at a loss to how confusing this is!!
    The current system I have is my boiler when installed by BG has a programmer (British Gas UT1) in the airing cupboard and that was then linked to a analogue thermostat in the hall ( 240v). The thermostat was removed and replaced with a Heatmiser programmer thermostat (digital). The old programmer in the cupboard was set to constantly on ( acting as a simple connector bloc I assume) and all the controls were then set up by the Heatmiser where the thermostat used to be. Now I’ve got 240 in the Heatmiser wiring when I only need low voltage for the Nest. I thought I could disconnect the wiring from the boiler utalise two wires, remove the old British Gas programmer and connect the two wires together to provide T1 & T2 to where the current Heatmiser is and connect to the nest. The heat link would be wired as is in the diagram to the boiler as it would normally be?
    Did that make any sense?
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