Old thermostat needs replacing to the digital one

Discussion in 'Electricians' Talk' started by TomV, Mar 12, 2018.

  1. TomV

    TomV New Member

    Hi, please could someone help me. I need to change this old thermostat to a digital one.
    No clue how to wire it. Please suggest.
    I am thinking to change it to Salus RT500 Programmable Room Thermostat or similar

    Attached Files:

  2. Dr Bodgit

    Dr Bodgit Well-Known Member

    Look like the red wire connected to '1' is the live and other red wire connected to '2' is the switched live (SL). The other two wires are likely neutrals that need to be connected together in a terminal/chocolate block, not connected to the RT500. The neutrals may not be needed at all but you first need to work out what they connect to before removing.
  3. JP.

    JP. Screwfix Select

    The unit is battery operated Doc and concur that the neutrals are not needed for the unit operation - however the neutrals should be as said be ''termed'' into a what? yes a Wago 2 lever 221-412 or chocs, aye chocs being 2nd choice.
    Dr Bodgit likes this.
  4. Bazza

    Bazza Well-Known Member

    Just as a sanity check. Often there is a circuit diagram inside the lid of the thermostat. Is there one? Post photo if so.

    Battery?? What, where, how?
  5. Dr Bodgit

    Dr Bodgit Well-Known Member

    Yes a wago is preferred over a choc block for connecting the neutrals, like this:

  6. JP.

    JP. Screwfix Select

    Hi Bazz -

    ''The RT500 requires two ‘AA’ alkaline batteries to function correctly. Ensure that
    the batteries are inserted correctly, paying careful attention to the polarity
    markings on the battery and next to the battery holders''

  7. Dr Bodgit

    Dr Bodgit Well-Known Member

    Its just like my thermostat, battery operated, programmable and is just a simple live "switch".
  8. JP.

    JP. Screwfix Select

  9. Bazza

    Bazza Well-Known Member

    AH yes, I know. But the OP hasn't chosen an RT500, he just said
    The way you wrote it, it looked like you were talking about the existing stat. (well, it did to me, anyways!)
  10. JP.

    JP. Screwfix Select

    Nice one Bazz..:)
  11. TomV

    TomV New Member

    Thank you for the answers!
    The old one does not have a circuit diagram.
  12. Bazza

    Bazza Well-Known Member

    I'm going with the Doc's advice in post #2 then.
  13. Wow, that's a weird one Tom!

    No accelerator used in that ol' beaut; it looks like a simple microswitch operated by that long bi-metallic strip along the top. I bet that wasn't very sensitive...

    Are there any earth wires present, Tom? Strange if not.

    It looks as tho' it's been wired using two separate cables, one of which is slightly thicker than the other (eg 2.5mm2 and 1.5mm2)

    Anyhoo, almost certainly it's as Bodge says; the thick red will be the LIVE (tho' it could be the switched live, but it doesn't matter in practice) and the thin red is the switched live. Do you have any way of testing this - even a nasty 'neon' screwdriver?

    The two blacks are neutrals and were not required in the old stat and also won't be needed in the new one (unless you decide to go for a rare mains-powered type. But most use batteries). However, I suspect they will need connecting together.

    Although not used, these blacks will need parking somewhere to keep them safe, especially since the B***** vote.

    If you go for the Salus RT500 - a perfectly good machine - then you will (I believe) find an 'earth' parking terminal in it. Ok, this isn't 'good practice', but if you DON'T have earth wires in your current stat, then I reckon you can park these two neutrals in the 'earth' park on the Salus. However, if you DO have earth wires (and I hope you do), then these will need parking in the provided terminal instead, and you'll need to obtain a separate terminal for the two neutrals as said before.

    I have seen some digi room and prog stats that do have neutral parking provided (as well as earth), and it's astonishing that more aren't like this since most folk will need to take care of their unneeded neutrals when fitting these. What an omission by many manufacturers.

    So, if you go for the Salus, it'll be thick red (or one of the reds) in to 'L', and the other red in to 'SL'.

    Other models will have 'COM' and 'NO' instead, or even 'A' and 'B', but the same applies.
  14. JP.

    JP. Screwfix Select

    Hmmmm parking neutrals in earth park location in place of non existent, aye maybe non existent cpc/s - sorry DA but dont agree with that technique m8..neutrals are classed as live conductors tbqh..:)
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  15. You are, of course, absolutely right JP.

    It was with a heavy proviso - no earth wires present - and with the acknowledgement that is was not good practice.

    However, if this were mine, then I know what I would do with this setup instead of leaving the earth terminals blank and trying to squeeze a wago in behind the unit.

    But, not 'correct'.
    Last edited by a moderator: Mar 12, 2018
  16. TomV

    TomV New Member

    Deleted member 33931 likes this.
  17. 'Welcome.

    Are there earth wires? If not, and if you are going to do my 'cheat', it would be good practice to place a blob of black paint over that 'earth' symbol on the Salus.

    Does that make sense?

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