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Honeywell T40 Thermostat Upgrade

Discussion in 'Plumbing and Central Heating' started by An.Dee, 3 Apr 2019.

  1. An.Dee

    An.Dee

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    Hi,

    I am planning to upgrade my Honeywell T40 Thermostat to a T4. I believe the T40 is usually a two and the T4 is a two wire.

    However I have 4 wires in my current T40, I believe I only use wires T1 and T3 into the new thermostat, which is straight forward.

    My concern is that my current T3 which is the switched live is a grey wire and that my T2 neutral is a black wire, which looking at other pictures are the wrong way round? I have followed the wires back to the wiring box and they are wired the same way as the thermostat.

    I just need confirmation, thee grey wire is ok to use. I do not have any problems with the thermostat or boiler, I would just like more functions.
     

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  2. Hello,

    Wiring looks ok to me. Neutral is usually blue, but years ago used to be black. The only thing that matters is in on 1, out on 3, 2 is neutral. If anything should have some blue sleeving on the black to show it’s neutral and as long as brown is permanent live.

    Hope this makes sense?
     
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  3. An.Dee

    An.Dee

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    Thank you for your reply.

    I have read black wires used to be neutral, but was unsure on the grey, and having seen pictures of of these thermostats being wired up totally incorrect, I wanted to check before attempting.

    I shall look for blue sleeving when I take the thermostat apart, and label if not.
     
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  4. ianmcd

    ianmcd

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    Never rely on colours in a heating wiring system, they are all different depending on who wired it up
     
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  5. DIYnot Local

    DIYnot Local

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