Nest Thermostat E with Honeywell CM900

5 Jul 2019
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United Kingdom

I’d like to apologise in advance as I’m a complete novice to this stuff. I’m trying to learn how to do wiring/installations and not rely on someone doing it for me so please be patient with me.

I’ve bought the new Nest Thermostat E to replace my Honeywell CM927 controller. I’ve located the receiver for the controller which is next to my boiler. When I went to install the new Heatlink E which came with the Nest E, the wire labels weren’t the same.

So my Honeywell receiver has wires for L N and then A B. The Heatlink E asks me for a C and NO wire. Through doing some research online, I’ve found that the A wire is the C and the B wire is the NO. My only question is, what happens with the L and N wire. Are they the power source to the receiver and will not plugging them into my Heatlink do anything? (Pics below)

Sorry if I the question I asked is simple, just trying to learn how this all works for the future. Thank you all

Honeywell receiver

Heatlink E
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Your Honeywell required a L&N to power it, your nestE uses 2x Batteries you will have to isolate the L&N and just use the two switching wires as you described in your post

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