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Fitting a nest 3rd gen to a modena combi boiler
- Thread starter Tetchysquire
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Erm.... first of all, why do you still have the Honeywell 927 connected? that should have gone first. You say you have wired up the Nest according to the instructions, but where in the instructions does it tell you to have a second thermostat connected? You will have now two devices in circuit trying to achieve the same thing!!
However, you can't just remove the Honeywell otherwise you will have an open circuit and the heating won't work. It needs to be decommissioned properly, by connecting the switching wires together. The Nest will work if your set the Honeywell to be permanently 'on' and at its maximum temperature. (assuming of course that you have made the right connections to the Nest Heatlink)
If that works, then the two wires in the Honeywell A and B terminals should be connected together either at their source, or at the thermostat if you are happy to leave it in situ. The 230v mains supply to the Honeywell can be disconnected and removed.
However, you can't just remove the Honeywell otherwise you will have an open circuit and the heating won't work. It needs to be decommissioned properly, by connecting the switching wires together. The Nest will work if your set the Honeywell to be permanently 'on' and at its maximum temperature. (assuming of course that you have made the right connections to the Nest Heatlink)
If that works, then the two wires in the Honeywell A and B terminals should be connected together either at their source, or at the thermostat if you are happy to leave it in situ. The 230v mains supply to the Honeywell can be disconnected and removed.
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No the Honeywell was how it was wired to begin with
I know it needs removing and won't work with 2 connected
I know it needs removing and won't work with 2 connected
Sorry I'm confused 
I don't know if you are asking, how to install a Nest..
or, for help because you have installed a Nest and it isn't working.
I don't know if you are asking, how to install a Nest..
or, for help because you have installed a Nest and it isn't working.
If the Nest is replacing the thermostat in the first photo. Then the L and N are a straight Swap like for like. Then the wire in A goes to the heating common terminal of the Heatlink (2) and the one in B goes to the heating call for heat (3) terminal of the Heatlink. That's all you need to do. Don't add any other links.
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