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Honeywell CM907 to Lyric T6

Discussion in 'Plumbing and Central Heating' started by Alex Terry, 22 Nov 2020.

  1. Alex Terry

    Alex Terry

    22 Nov 2020
    Thanks Received:
    United Kingdom
    Hi All,

    I'm trying to upgrade my existing Honeywell CM907 thermostat to a newer Honeywell Lyric T6 but can't quite figure out how to translate the wiring from one to the other. The wiring diagrams are attached - As you can see the CM907 has two wires going to it from the boiler but the T6 also needs a Live and Neutral from the boiler, does this mean I have to completely rewire?


    Screenshot 2020-11-22 at 17.00.34.png Screenshot 2020-11-22 at 17.00.56.png
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  3. stem


    20 Jul 2005
    Thanks Received:
    United Kingdom
    The CM607 is battery powered so the wires connected to A & B are only the switching wires, which also correspond with A & B in the Honeywell receiver box.

    However, the Honeywell receiver box isn't battery powered so it needs a 230V supply connecting to its N & L terminals to provide it with operating power, this should come via the same fused connection unit that supplies the boiler. You can pick this up from the boiler as shown in the diagram you posted, or directly from the fused connection unit supplying the boiler

    You need to be aware that some boilers have their wiring terminals contained inside the room sealed part, which means that only an RGI [Gas safe] engineer should access them as they will need to carry out the necessary safety checks afterwards to make sure that it is properly sealed up again afterwards. If your boiler is like this and you want to DIY, then the connection should be made to the fused connection unit.

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