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Hive wiring removing old room thermostat

Discussion in 'Plumbing and Central Heating' started by Greeny12m, 16 Sep 2019.

  1. Greeny12m

    Greeny12m

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    Hi guys,

    Hoping I can sort this out without bringing in a tradesman.... I'll try to include as much info as possible.

    I have a Suprima boiler and Hive thermostat which I installed soon after moving into my new house, the whole system worked well over the winter for both CH and HW. The system had a very old (dark brown dial with Fahrenheit graduation) looking wired room stat right by the front door which we effectively bypassed by setting to the highest temperature setting. The Hive overrode this at the receiver box which replaced the British Gas (i think it was) programmer which is in the kitchen - as is the boiler.
    Over the summer with the CH off we have been decorating, taking rads off the wall for painting etc. I figured I could remove the room stat and bridge the connection in the Honeywell junction box (in the loft with the tanks/pump/3 port valve). However when I opened it up I could not work out which wiring plan the installer had used (if I am honest it is a total sh*tshow) there are cables going into connections on the connector block which are not used in any wiring diagram I could find.
    No worries - I will just remove the room stat and bridge the terminals of the 2 core cable that was connected to the stat - work out later. But NO! CH now will not kick in when boosted in Hive app/receiver box despite the only difference being the bypassing of the room stat.
    To try and identify which cables in the loft correspond to the room stat I did a continuity test using a basic multimeter (ran a cable from room stat to the loft). But with this method only helped to identify one terminal of the two that connected to the old room stat.
    I must therefore assume that the room stat is connected directly to the programmer terminals or the boiler (no two core cables end up in the loft), the power was off during continuity test so perhaps the circuitry in the boiler.

    Does any of this make sense? am I missing something? how can I bypass the old room stat wires?

    thanks!
     
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  3. stem

    stem

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    The old thermostat can't simply be disconnected as this would leave the heating wiring 'open circuit' and it would not operate, the integrity of the circuit needs to be maintained. As not all thermostats are the same, or indeed wired the same, the specific instructions vary from installation to installation. In the diagram below, I have marked the terminals Neutral / Live / Switched Live to indicate their function, but the thermostat manufacturer may have identified their terminals with sequential numbers or letters. So, whilst the steps are the same, some working out will be required in each case.

    The room thermostat is just an on / off switch so when set to the highest setting will be permanently 'on'. When the thermostat is removed the switch terminals need to be bridged to achieve the same thing. It appears you are on the right lines, but something has not been done correctly.

    1. Look at the wiring diagram for your make/mode of thermostat that you are removing. If you don't have the instructions for it, a diagram is usually printed inside the lid. This will show which are the two switching wires, and which is the neutral wire. (If there is a neutral present. Not all thermostats need or have one fitted)

    2. Trace the cable from the thermostat back to its origin.

    3. Take take a photo, or make a note of where the switching wires are connected at their origin.

    4. Disconnect all of the wires going to the old thermostat and remove the cable and thermostat. All other wires to remain in place.

    5. Insert a wire link between the terminals where the two switching wires have just been removed from, so that they are now electrically joined together.

    Decomission stat 2 Model (1).jpg

    If you need any further help, provide details of the make / model of the existing thermostat, or post a photo of its wires and connections internally.
     
    Last edited: 16 Sep 2019
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  4. Greeny12m

    Greeny12m

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    Thank Stem,

    That is what I thought needed to be done and had attempted to do without success. The room thermostat that was removed only had a 2 core cable the led back to the wall so no permanent live. Sadly the stat is currently "missplaced" so I could not tell you the model, i think you could just assume that is was '60-'70's era. Bridging the cables in the hallway (equivalent to what you suggested) results in boiler no-fire despite Hive activation.

    I have found my notes I made while I was in the loft that might help someone decipher what wiring plan (if any) was used and what might need to be done:

    upload_2019-9-16_19-37-59.png
    I think that one of the room stat cables had continuity with the grey cable coming from the boiler.

    Any insights?

    Thanks
     
  5. stem

    stem

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    If there were only two wires, then the thermostat information isn't necessary, one will be the live supply and the other the switched live. (no neutral)

    Unfortunately when it comes to wiring of heating systems the colours of the wires for each function are chosen according to the personal preferences of the installer, and the materials used, sometimes blue and black wires are used as a neutral, some times as live, so it's dangerous to guess the function of a particular wire from its colour, it needs to be determined by what is connected to each end of it. Also, although there is a general method of wiring systems up again there are many variants as to where the control signals are picked up from depending upon the layout of the heating components in your home.

    First of all, check the work that you have done, in that the conductors are securely in the terminals and that adjacent wires haven't been disturbed or loosened.

    My next suggestion would be to put the wiring back exactly as it was, but with the two wires where the thermostat has been removed joined together. Then once the heating is working start again. You need to do this, because it would appear that you may not have identified the room thermostat cable correctly and may have disconnected another part of the wiring, if so, that will need to be reinstated first.

    Once the system is working again, you may be able to identify the room thermostat wires by where they are connected. Usually one of the room thermostat wires will be connected to the live heating supply from the Hive (terminal 4 of the dual channel version) of the programmer/timer, and the other will go to the brown wire of the 3-Port motorised valve (I assume this is what you are calling a '3 Port Switch') once you have identified what you believe are the thermostat wires, note carefully where they are connected and remove them, to be sure you have the right wires they can be tested with a multimeter. The wires may not go directly from point to point, there maybe a junction box somewhere in between so their colours may even change from on end to another.

    If you can't reverse what you have done and get it working again, then you will probably have to engage the services of a professional who can inspect / test the wiring and work out what has been done.
     
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  6. ianmcd

    ianmcd

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    @stem , totally agree withe the colour of wires in heating systems and never trust the colour, manus have to take some blame too, not sure if you have wired any of the Grundfoss Conlift pumps, they have a LNE, flex then an alarm 2 core flex which both cores are Live but colored brown and blue, bound to be many mistakes with installers wiring that up, it is simply an in series switch so both cores could be the same colour without any problems
     
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  8. Greeny12m

    Greeny12m

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    I semi-solved my problem. Turns out my initial investigations on the Honeywell box in the loft had left one of the cables with a bad connection so the 3-port valve was not getting the signal.:cautious:Shorting the old room thermostat connections now kicks the heating in.(y)

    Only issue now is that connection 4 on the hive back plate goes directly to the old stat rather than via the Honeywell wiring box... So as far as I can tell I will just have to just bury the cable in the wall and forget about it. Unless anybody has any other good ideas?
     
  9. stem

    stem

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    A couple of suggestions for you:

    Option 1. As you have found the origin of the thermostat cable, and you can see that one of its wires goes to Hive 4. Then if you can see that, you should also be able to see where the other wire goes. Then it's just a matter of removing the thermostat cable and linking Hive 4 to wherever you have just disconnected the other wire from.

    So:

    1.jpg

    Becomes

    2.jpg


    Option 2. Remove the thermostat cable and connect the white wire from the motorised valve directly to Hive 4.

    If you decide not to do this and do 'bury the cable in the wall' you should really connect a thermostat to it and use it as before. The wiring regulations state that wiring should have an 'accessory' connected to indicate the presence of a concealed live wire in the wall. The wires must run horizontally or vertically from the accessory in what is known as a Safe Zone. You can find more info on this here.
     
    Last edited: 20 Sep 2019
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  10. ericmark

    ericmark

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    Although there is no colour code for installation cables, the three port valve do tend to have a colour code, I will stand to be corrected, but I think a three port valve means you have either a Y plan or W plan most likely Y plan.

    So the valve blue = Neutral, Green/Yellow = Earth, White = output from wall thermostat, grey = N/C contact of cylinder thermostat, and orange goes to boiler and possibly pump.

    Basic idea with most motorised valves is the thermostat works the valve and the micro switch inside the valve works the boiler and pump so boiler will not fire up until valve is open. However the three port is slightly different as the default is DHW so all three connections used on the cylinder thermostat com, N/O and N/C some people are rather naughty, it should be a 4 core cable to the cylinder stat, but I have seen many times where people have used the earth core and only used three core cable, so green/yellow is some times a live wire, be careful.

    Testing wires can give some odd results, as inside the motorised valves there are quite a few components mid-position-valve.jpg so you can get back feeds, I note the Nest wiring diagram for Y plan shows the valve colours, don't know what Hive shows. But if No 4 (CH on) goes to white on motorised valve it should work.
     
  11. Greeny12m

    Greeny12m

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    Thanks for the advice about leaving a live wire in the wall.

    As the honeywell junction box, the cylinder, 3-port valve and the pump are all within a few feet of each other in the loft I was able to work it all out :cool:.

    Option one is what I was hoping to do but is tricky because of the locations of each component and no spare cores going from the programmer to the loft. I think what I will have to do is to lift the carpet/floorboard in the room above the old room stat and try and bridge the connections there.

    Thanks again!(y)
     
  12. ericmark

    ericmark

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    I know what you mean, I found just two wires between main house and flat where the boiler is, and MDF flooring so big job to route new cables, as I hunted I found Nest Gen 3 which has just two wires from thermostat to heat link so I can switch both DHW and CH on/off with two wires, well also from any internet connected PC but wanted to control in house when all pumps, valves, and boiler in granny flat originally a garage under the main house.

    Hive for me would have been better, but it does not have volt free contacts, in my case also a point where old programmer was located, I have put a blanking plate over the connection so still clear that wires run there, and since now only 12 volt DC there is no danger anyway.
     
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