Underfloor heating temperature sensor wire - can I fix it?

Discussion in 'General Chat' started by InvisibleDuncan, Apr 18, 2018.

  1. InvisibleDuncan

    InvisibleDuncan
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    Okay, this is a long shot because it's a very specific question and this isn't a DIY forum, but I've seen that there are quite a few people on here who really know their onions, so I thought I'd give it a try.

    While trying to put on a new control panel for the electric underfloor heating in my kitchen, I managed to pull the end off one of the wires that come out of the temperature sensor.

    Wires.png

    The bit I pulled off the green wire is the same as the end of red wire (except for the colour, obviously.

    Does anyone know whether it would be possible to reattach the end, or whether I can just strip some plastic off the green wire and use the internal wire directly to insert into the panel?

    This is why I should never be allowed to do DIY.
     
  2. MrSossidge

    MrSossidge
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    How much is a replacement sensor cable. They should be replaceable.
     
  3. IronGiant

    IronGiant
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  4. ChuckMountain

    ChuckMountain
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    Depends on whether you can get the other end out or not. It could well be fixed under the floor and trying to feed back the sensor to the right place would be a right pain in the bum.

    From the photo this is the control unit end as @IronGiant says it requires a blade terminal connector of the right size and cable thickness and a crimp tool something like this.

    https://www.amazon.co.uk/Draper-Red...TF8&qid=1524054153&sr=8-4&keywords=crimp+tool

    Inserting the bare wire should be avoided as you cannot guarantee the connection.
     
  5. InvisibleDuncan

    InvisibleDuncan
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    Thanks guys - for an AV forum this place is incredibly versatile. :thumbsup:

    I've tried to gently tug the sensor cable out, but I think it might have been grouted into place by the installer. I'd rather avoid replacing it if possible; I'm worried I might break it if I pull too hard (as I managed with the other end) and won't then be able to put a new cable in the same place.

    I still have the other connector as it pretty much just slipped off into my hand. If I were to strip a bit of the insulation and get hold of one of the crimping tools, do you think I should be able to reuse it... or should I just order a new one?
     
  6. noiseboy72

    noiseboy72
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    How does the connector fit into the control box? If it’s a screw terminal, just strip, twist and screw in. If not, then yes, just strip about 5mm off the sheath and give it a crimp.
     
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  7. ChuckMountain

    ChuckMountain
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    True, that's going to be easiest way. Don't remember seeing many with that type of connector so it might be just so its easier for the screw to get something to grip on.

    You can potentially reuse the old connector you might to uncrimp it a bit but sometimes its easier to get a new one.
     
  8. aVdub

    aVdub
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    Can you take a photo of the other end. You may be able to crimp or solder the wire back...
     
  9. InvisibleDuncan

    InvisibleDuncan
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    Yep, it's a screw connector on the control panel. I''ll give it a try with the strip, twist and screw suggestion first.

    Thanks for all the help, folks - it's much appreciated. :)
     
  10. InvisibleDuncan

    InvisibleDuncan
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    I'm not at home at the moment so can't take a picture of that bit. Hopefully if I follow the advice given above I'll be able to sort it - although it probably won't be until the weekend now.
     
  11. nheather

    nheather
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    If it is like the one I have, and I’m sure it is, then the wires just go into screw-down terminals. The ferrule just makes that a tiny bit easier but you don’t need it.

    You could leave the red ferrule in place but personnally I wouldn’t as I’d prefer the exposed green and red wires to be the same length, so this is what I would do.

    Strip back the outer grey insulation a little so there is more green wire exposed (about the same as the red wire including ferrule is now.

    Cut the red so it is the same length as the green wire.

    Strip back the insulation of the red and green wires.

    At this point you could fit replacement ferrules, but really not needed, you can simply insert and screw down the wires as they are.

    If you have ever fitted a mains plug it is pretty much a similar approach.

    BTW the floor sensor is mostly a safety feature to detect if the floor pads are getting too hot when something is seriously going wrong. For the most part the temperature of the room is controlled by the sensor in the wall controller. It would still work without the floor sensor would just be missing a safety feature.

    Cheers,

    Nigel
     
  12. ChuckMountain

    ChuckMountain
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    No real need to have lengths identical other for ease of screwing in. It won't affect the temperature reading.

    I appreciate yours maybe a different model but my UHF can use either underfloor or air or both to set the desired temperature.
     
  13. nheather

    nheather
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    Agreed, I only said that because

    1) I have OCD :)

    2) I suspect the green wire is a little too short as it is, so you will have to strip back some of the grey insulation to make it longer and if you are doing that you may as well make the red and the green the same length.

    And yes you can set the controller to use floor sensor only, wall sensor only, or both, but in my experience floor only does a really poor job, and wall only and both behave about the same, so much so I suspect algorithm is only using the wall sensor for temperature control.

    I’m not saying not to fit the floor sensor, absolutely fit it, just explaining what it does.

    Cheers,

    Nigel
     
    Last edited: Apr 18, 2018
  14. InvisibleDuncan

    InvisibleDuncan
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    Great stuff - thanks, guys.
     
  15. ufo550

    ufo550
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    Dear me what a lot of tosh. The manufacturers of such equipment usually provide a soldered end (not the correct terminology, excuse me!) or sometimes a ferrule. That's to ensure the multi flexible strands of a flexible cable end up securely terminated.

    You just need something like this;

    upload_2018-4-18_18-1-59.jpeg

    By the way, don't try and pull he sensor out, as likely or not you won't get it back in its flexible conduit. Something other people find out when the sensor packs up, and trying to replace it.
     
  16. IronGiant

    IronGiant
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    What a lot of tosh, it's clearly a 2.8mm blade connector... :p

    But yes, I wouldn't try and pull the sensor out.
     
  17. ChuckMountain

    ChuckMountain
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    More tosh :)

    Its a blade connector because the connector on my equipment and the other ones I have seen are designed to take either stranded or solid core. Its a screw down clamp like these although a different colour :) This has the benefits of when stranded it will flatten it down and make connection with all the strands...

    A flat connector will have a greater surface area in connection ... :nono:

    [​IMG]
     
  18. Trollslayer

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    Crimp the replacement connector on - do not solder it because the insulation could melt and it may be that changing the metals involved could change the cable behaviour. Not very likely but as crimping is easy no need to risk it.
    The crimp connector is standard, no need to buy a fancy one.
    Farnell stock a wide range:
    http://uk.farnell.com/w/c/connector...nals-splices/pin-terminals?range=inc-in-stock
    This one looks pretty close:
    http://uk.farnell.com/amp-te-connectivity/165143/terminal-wire-pin-22-16awg/dp/1863544
     
  19. ufo550

    ufo550
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    You guys. The reason as previously state is to ensure the multi strand wire of a flexible cable is suitably terminated, hence moulded plugs for appliances, and said finished ends for such cables. Its not the end of the world in those terminations are not provided, there's lots of flexible cables terminated without ferrules etc. How many people successfully put a plug top on the end of an appliance without issue.

    However, a simple ferrule when terminating in accessories is more than adequate. Crimp connections are often used where the termination might be under strain. Inside a back box, this is unlikely.
     
  20. ChuckMountain

    ChuckMountain
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    You made your point the first time, reiterating it does not change it.

    The blocks are above are substantially different to a 13amp plug. On the plug you have a screw that is responsible for keeping the wire in place against the contact. I would agree it might be more sensible to solder them in that case.

    The green blocks have a parallel jaw mechanism that comes together flat and will terminate both. The stranded connection may well have a lower resistance as you have more surface area than a solid\soldered connection.

    Hence the reason a flat connector was used in this way.

    Terminating directly onto bare wire eliminates an additional joint in this case.
     
  21. MSW

    MSW
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    Alluded to before but, would it bit a lot simplier / easier to change your underfloor heating thermostat / control unit to work on “Air” Temp rather than floor Temp.

    In the unlikely event your current unit only works on for temp a replacement unit that will do either “Air” or “Floor” is relatively cheap
     
  22. noiseboy72

    noiseboy72
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    This seems to have come a long way from " I can just strip some plastic off the green wire and use the internal wire directly to insert into the panel"...
     
  23. ChuckMountain

    ChuckMountain
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    Oh good grief. Regardless of me and @ufo550 discussion on merits of to crimp or not to crimp this is an easy fix ! :nono:

    All this is a regular cable with a thermistor at the end buried under the kitchen floor.

    All that needs to be done is it reconnected to the thermostat by stripping part of the wire, optionally putting a flat crimp connector on and tightening up the screws. Follow the wiring colours if there are matching ones but if not it should not matter which way round it goes.

    Swapping to a cheap thermostat is an unnecessary amount of expense and work. You also need to ensure it can handle the load, not all of them will do. :facepalm:
     
  24. ufo550

    ufo550
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    My point is that such flexible stranded cables are often terminated without such diligence to no avail. However, good practice and workmanship suggest the use of ferules etc, or suitably provided terminals are you have suggested.
     
  25. ChuckMountain

    ChuckMountain
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    Yes happy with either or ;)

    Not happy with suggestion of swapping thermostat to solve OPs problem :D
     
  26. noiseboy72

    noiseboy72
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    13A plugs should always have ferrules, as the screw rotates as you tighten it up and damages the strands. You don't need ferrules or crimps for the compression type connectors, but if you intend to connect and reconnect regularly it's very good practice. You also need to ensure that all strands are captured and that shorting is not possible.
     
  27. MSW

    MSW
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    Forgive me
     
  28. MSW

    MSW
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    My apologies
     
  29. nheather

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    It's the AVF way.

    Why go for a two minute, cost free fix that is totally viable, when you can wade through pages of discussion, spend hours researching the right ferrule, spend some quids ordering the selected ferrule, wait days for said ferrule to arrive, then realising that you don't have a crimp tool post whether it is okay just to crimp with pliers. A five page discussion ensues about the correct type of crimping tool which results in you ordering the super deluxe automatic crimper at a cost for £19.95 and waiting more days for it to arrive.

    So eventually, 10 days after declining a free two minute fix, you achieve pretty much the same thing having spent in excess of £25 but smug that Isambard Kingdom Brunel would be proud of your engineering solution.

    Cheers,

    Nigel
     
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  30. outoftheknow

    outoftheknow
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    The jury is out on that - he may have broken the connection to the thermistor whilst gently tugging the wire...........

    Seriously OP screw or crimp or twist or flatten the stripped end of that broken wire to connect it where it was and report back if the sensor is knackered or (9,999 times out of 10,000) it receives the temperature reading and you have a toasty floor/room.

    We have heating under our ensuite tiled floor and it only reads floor temperature. Purely for no cold feet on the tiles so reading air temp (we have central heating for that) is pointless. If the OP uses it for that same purpose the swapping to read air temperature really will be pointless too.
     

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