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Nest Thermostat Installation

Discussion in 'Plumbing and Central Heating' started by chalky74, 28 Nov 2015.

  1. chalky74

    chalky74

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    Hi,

    Just recently purchased our Nest thermostat, haven't tried wiring it in yet but have been looking at the manual and just trying to get it right before I start.

    Currently using the Honeywell CM921 thermostat and relay box with a Baxi Duo Tec combi boiler.

    According to the Nest manual I need connect a Live and a Neutral which I get and can identify easily in the CM921. But also it says I need to connect a "call for heat" (2) and a "common" (3). The but I don't understand is there are two wires in the CM921 that are connected to a terminal block labelled A and B.

    My question is, is A in the CM921 "call for heat" or is it the wire connected to B. Presumably if A or the B wire is call for heat the other would be common?

    Any help would be appreciated.

    Thanks
     
  2. nortonj

    nortonj

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    Yes a is call and b is common.
    I think it will still work if wires reversed
     
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  4. D_Hailsham

    D_Hailsham

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    Er no, it's the other way round. But, as you rightly say it doesn't matter if the wires are reversed.
     
  5. nortonj

    nortonj

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    Thanks for pointing that out.
     
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