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Help with Thermostat wiring, please!

Discussion in 'Plumbing and Central Heating' started by DickyRobbo, 21 Nov 2020.

  1. DickyRobbo

    DickyRobbo

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    Hi all,

    Really struggling wiring up some thermostats.

    I have a combi boiler. The thermostat I removed was wired in as below;

    [​IMG]

    A grey wire and exposed earth wire weren't connected.

    Here's the instructions.

    [​IMG]

    Now I tried connecting as the instructions say, the thermostat powers on etc but it does not kick the central heating on!

    Found a user who connected as my picture below, doing it that way for me provides no power to the thermostat and it doesn't turn on or do anything!
    [​IMG]
    Can anyone advise? What am I doing wrong? The only way the unit powers up is with brown in 1 and black in 2.
     
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  3. ianmcd

    ianmcd

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  4. stem

    stem

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    It looks like the original thermostat was battery operated and new one is mains powered is that correct?

    What is the make / model of the old thermostat?

    If you have used the existing wires I assume that the brown and black wires now in terminal 2 & 4 were those connected to terminals 1 & 2 of the old thermostat. Is that correct?

    Is the brown wire actually a 230V live? (I ask because some boilers use 24v for their control circuits) this would need to be confirmed by someone competent to test it with a multimeter. Note: If your boiler is one that is wired for 24v you should never insert a link between a 230V terminal and a 24v one.

    If there is some form of time control elsewhere then you will probably find that will need to be set to be permanently on 24/7 otherwise it may turn off the power supply to the new thermostat

    A bare wire link is a very bad idea, it can easily short across the other wires. This is dangerous and could cause expensive damage to your boiler and / or thermostat.

    Then there is a grey wire connected to the N terminal. That has appeared from somewhere. What is that wire connected to at its other end, if anything? [Note: Some combi's have their wiring in a room sealed compartment, if you need to open up such a compartment to find the other end of the wire do not proceed, this should only be opened by a registered gas installer who can check that it is properly sealed up again afterwards]
     
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  5. DickyRobbo

    DickyRobbo

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    What is the make / model of the old thermostat? Moesgo Wifi Smart Thermostat

    Brown wire is 24v just confirmed. So I shall remove link.

    Not sure on other controls. But wires are as follows. At boiler;

    [​IMG]

    At switch;

    [​IMG]

    Old thermostat was battery operated, didn't use the grey wire. Assumed it was the control wire.

    I've made it all safe for now.

    Just to add this is a 2 zone system with zone valves.

    [​IMG]

    [​IMG]
     
    Last edited: 21 Nov 2020
  6. ianmcd

    ianmcd

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    Do not mean to sound rude, but you need to get someone in, you have absolutely no clue what you are doing , you can cause and may already have caused some really expensive damage when you get these things wrong
     
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  7. DickyRobbo

    DickyRobbo

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    Nah no damage. Put the old one back on till I can figure it out, everything working fine. I wouldn't say absolutely no clue. Was just looking for a little help thats all with the correct positions on the thermostat. Sorted if now anyway.
     
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  8. stem

    stem

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    What you say doesn't quite add up. You have a two zone installation, but only one thermostat!!? I'm not sure how that would work. You now tell us it has motorised valves, so the thermostat (or thermostats) will be controlling the motorised valves and not the boiler. So even if the boiler is 24v, motorised valves are usually 230V.

    If one of these is the other end of the grey wire, as I suspected it's not connected to anything.

    1.JPG

    The Brown and black wires from 1 & 2 of the old thermostat will go to terminals 1 & 2 of the new thermostat. Then it will need a new 230V supply to power the thermostat. This should be from the same 3A fused spur that provides power to the boiler to the new thermostat terminals 3 (N) and 4 (L)

    However, I agree with @ianmcd it is probably best for you to get a professional to do it for you.
     
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