Neutral not connected in Honeywell T6360 thermostat

Discussion in 'Electricians' Talk' started by Marcos Scriven, Feb 14, 2018.

  1. Marcos Scriven

    Marcos Scriven New Member

    I'm about to replace my thermostat, but was surprised to find no neutral connection.

    IMG_3624.JPG

    It seems to function ok though - when the thermostat is on, I see 230V AC across T1 and T3, and the boiler turns on.

    It looks like the blue wire was in the right position, but is unscrewed and the metal end of the wire removed.

    I can measure 190V AC from T1 to the expose tip of the blue wire. Should it have been connected? Is it just a mistake?
     
  2. unphased

    unphased Screwfix Select

    If you can verify that the other end of the blue wire is connected to a neutral then it should really be connected. It is something to do with temeperature gradient on this type of stat that required the neutral to operate it. It makes the room stat more accurate I believe. However, if you are changing it there may be no requirement for it in some types of thermostat.

    https://www.honeywelluk.com/product...perature-onoff-control/T6360-Room-Thermostat/
     
    Last edited: Feb 14, 2018
    Marcos Scriven likes this.
  3. Marcos, if you are only measuring 190V between the bare blue wire end and the Live, then I wouldn't connect it as something is amiss and that may be why it was removed in the first place.

    Also, you should not be detecting 230V between T1 and T3 when the thermostat is turned up beyond its 'click', only when it's set to below room temp (ie the themo is 'off').

    Are you planning to replace it? If so, will it be a battery type (ie '2-wire')? If so, you can ignore that blue, folding over the end and taping it for complete safety.

    If, however, you want to keep that stat or replace it with a new 'mains'-powered type, then we'll need to investigate where exactly that blue is going to at the other end!

    Do you have a wiring centre (a rectangular box with a lid that all the cables are going to)? If so, could you turn off the power, open the lid and take a photo? Can you work out which cable is the 'stat one?
     
    Marcos Scriven likes this.
  4. seneca

    seneca Screwfix Select

    Yes it should be connected, there is a small heating device in the stat which senses the ambient temperature (accelerator I have seen it called) and makes the stat more sensitive to temp changes than just relying on the bi-metal strip. Many plumbers don't understand this because to them a thermostat "is only a switch"!
     
    Marcos Scriven likes this.
  5. Marcos Scriven

    Marcos Scriven New Member

    Thanks all for the responses - nice to know for the future, but as it turned out the new one didn't need neutral (only COM and NO), and so I just stripped the end and put it in one of the parking terminals.

    There was no box, just a cable coming out of the wall (annoyingly to the side, meaning on the new one I could only drill a screw hole for one side).

    IMG_1907.JPG IMG_9023.JPG
     
  6. By 'wiring centre', I mean at the other end of that cable, usually near where the boiler is (or hot cylinder).

    Anyhoo, with a 2-wire replacement stat, you certainly don't need that Neutral.
     
    Marcos Scriven likes this.
  7. Well done for resolving it - Happy New 'Stat :)

    (You are 100% sure that these are 'parking' terminals, and the top unit doesn't have any pins coming out of it that engages with them?)
     
    Marcos Scriven likes this.
  8. seneca

    seneca Screwfix Select

    I would think that only the one marked NC is no connection? (only a guess though)
     
  9. Risteard

    Risteard Screwfix Select

    Or perhaps Normally Closed like it usually means...
     
    leesparkykent and Marcos Scriven like this.
  10. Marcos Scriven

    Marcos Scriven New Member

    Yes as @Risteard says, NC means 'Normally Closed', which means the 'normally the relay is closed, completing the circuit, and turning the device on', which is what you'd have for aircon. NO is 'Normally Open', and does the reverse (only closes the relay to turn on boiler when room below temp).
     
  11. Marcos Scriven

    Marcos Scriven New Member

    Yep - it's from the instructions (as an amateur DIYer I'd have probably just called the 'spare terminals', but I like the sound of 'parking slots'.

    You were right too about the box near the boiler, there's a surface mounted box, but it's behind a washing machine. Glad I didn't have to go poking around in there.

    Screen Shot 2018-02-14 at 13.05.02.png
     
  12. It's nice to see the Tado provide these terminals - some 2-wire stats don't have them which is a nutty omission.
     
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  13. unphased

    unphased Screwfix Select

    Yes, I agree, it is a useful addition to allow redundant wires to be parked. The usual trait is finding them cut which helps nobody f they are required again in future.
     
    Marcos Scriven likes this.
  14. leesparkykent

    leesparkykent Well-Known Member

    o_O
     
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