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Baxi Combi 105 HE - Honeywell CM927

Discussion in 'Plumbing and Central Heating' started by s11DIY, 8 Oct 2008.

  1. s11DIY

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    Hi there,

    Hope someone can help me please.

    In my house I got Baxi Combi 105 HE for heating and hot water. I am planning to buy "Honeywell CMT927 (CM927) Wireless Programmable Room Thermostat". Is that the right choice? Where can I buy cheap?

    Is there any possibility of guiding me so that I can install myself.

    Much appreciated.

    Thanks

    Smith
     
  2. Rob

    Rob

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    You could buy online or try your local plumbers merchant/

    It will come with installation instructions.

    Unit seems ideal. Just remember if you have an existing timer to either link it out or leave it on 'constant'
     
  3. s11DIY

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    Today I checked the manual for my baxi combi boiler. I think I have to buy 4 core electrical cable to do the connection of CM927 with combi.


    It would be help it somebody can confirm the connection, which wire going where please.

    Much appreciated.
     
  4. D_Hailsham

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    Yes, you do need four wires to the CM927 receiver: Line, Neutral, A Terminal and B terminal. If you want a single cable you will find that you will have to buy a 4-core plus earth (available from B&Q); but there is nothing to stop you using two twin-cores (without earth) if you want to. Just makes it easier if you have four separate colours.

    You wire it as shown in diagram 4b in the installation instructions. L and N of the receiver can connect to any permanent mains supply, including the L and N terminals in the boiler. The A and B terminals connect to 1 and 2 on the boiler. If there are any wires already connected to 1 and 2, or a link between them, remove them; this will disable any existing clock and thermostat. The only exception would be if you have a frost stat (boiler in garage).
     
  5. s11DIY

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    Thankyou very much for your swift response. Just confirming, if I get the 4 core wire plus earth, where the earth wire connecting to.

    My combi boiler is fitted in the kitchen, so I think it should be fine. Does it means the frost stat will not work? Any complications.

    Last thing is CM927 good wireless thermostat? I have not bought it yet. Do you recommend any other or it is fine...

    Hopefully the reciver does not need anything else to be fitted on wall.

    Much Apprecited.. Thanks once again.
     
  6. D_Hailsham

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    The earth wire is not needed - it just happens to be part of the the cable - so there is no need to connect it at either end. I would cut it back to the outer insulation, so that no one thinks it has been forgotten/disconnected.

    If the combi is in the kitchen, you won't have a frost stat; so no complications.

    Probably the best wireless stat on the market.

    Make sure follow the instructions about location (page 3, diagram 1). It is also a good idea to check the communication between the two units of the CM927 before fixing to the wall. I did this by attaching a long lead to the receiver with a 13A plug on the other end. It's then easy to hold the receiver against the wall and check it receives OK from the proposed transmitter location.
     
  7. s11DIY

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    You Wrote

    So this means, only two wires are going to the boiler from the receiver connecting Terminals 1 and 2, and other two from the receiver can be connected to any of the main supply. It is not necessary to connect them to L and N terminals in the boiler.

    Please clarify, sorry for asking you again and again.

    Hopefully I dont need anything else except screws to fix the receiver on the wall??

    Thanks for helping me out.
     
  8. D_Hailsham

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    That's correct. The L and connections of the receiver do not have to be taken from the boiler; but if you are using a 4 core+ earth cable it is much easier to do so. If you want to use a separate L and N connection it should be controlled by the same switch/fused spur which turn the heating system off

    Just screws and rawplugs, if necessary.
     
  9. s11DIY

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    Thanks for helping so far.

    Today I went to buy 4 core wire. The salesman was asking me for what sort of AMP you looking on the wire. I said I want it for Mains, but he said we got some 4 core wire for door bell something like that which he think it is for very low voltage usage. Then he showed me another 5amp 2 core wire. I thought to first consult with you then buy the appropiate one tommorrow.

    Thanks once again.
     
  10. D_Hailsham

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    I was out all day yesterday, so only just read you reply. Have you managed to get the correct 4 core cable? If you have a B&Q near you or a plumbers merchant they will have what you want. B&Q sell it in pre-packaged lengths (Tower Brand), rated at 10amp, which is more than adequate. You need the 5-core version (4 plus earth).
     
  11. s11DIY

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    Not a problem mate. At least you replying and helping that is more than enough. To be frank B and Q is quite far from my place, i did not go there, but went to town to shop in general but as you said no body stock 5 core cable. One thing I checked the BandQ site with the following url it is around 12 pounds for 5 meters. At the most i need just 2 meter.

    http://www.diy.com/diy/jsp/bq/nav/n...refview=search&ts=1223826767735&isSearch=true

    They can't send in post.

    I searched a bit seems bit cheap option with delivery just 6 quid for 2 meter. What you think? Check the url below, I am talking about the last one with 10 amp.

    3185Y 1.0mm 5 Core Pvc Flex


    http://www.tlc-direct.co.uk/Main_Index/Cable_Index/Flex_White_3/index.html

    cheers
     
  12. D_Hailsham

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    You do not need 10 amp cable. The first one at 99p per metre will do fine. You need to check with TLC what their minimum order value is.

    OK, B&Q is too far away; but I would be surprised if your local plumbers merchant or electrical wholesaler did not stock the cable. They will usually cut it to length for you.
     
  13. s11DIY

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    Cheers, I was in the impression, that I need 10amp cable. So this means anything between 3amp to 10amp wil do the job. I opened the boiler yesterday just to check the connections. Seems pretty straight foward.

    I will go from 3amp cable.

    What I am thinking is use two 2core 3amp cables. One for the terminals and other one for the mains supply. I dont think there is too much room for the four wire to go into the boiler, otherwise I have to make another hole or widen the existing one. Is it ok to plug the mains from the thermostat receiver to the plug where the bolier is connected? Should not make any difference.

    Cheers..

    Will be done today. Yesterday saw few 3 amp - 2 core cables branded as Tower in willkenson store.
     
  14. D_Hailsham

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    Two 2-core 3A is fine.

    Yes you can supply the receiver from the boiler plug; although my preference would be to use the L and N terminals in the boiler - looks neater.
     
  15. stephendbn

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    Hello
    Hoping someone can help/point out where I'm going wrong.
    I've been reading this thread and have fitted a CM927 to my baxi 105HE following the instructions, & advice found on this site. I've done everything exactly as per the manual but it doesn'y seem to work! I've removed the link between terminal 1 & 2 and done all the wiring correctly. The CM927 remote thermostat communicates with the reciever & I can hear the relay clicking in the receiver when I turn from 'off' to 'manual' but it doesn't stop & start the boiler.
    I've got the switch on the boilers mechanical timer set to the 'I'/constant position but this just makes the boiler on constantly as before. I'm pretty sure I've tried every combination of settings on the boiler panel but nothing seems to make the boiler respond to the CM927, everything seems to be wired & meters out right - I'm thinking that maybe there's something wired wrongly in the boiler or that something else is wrong with it - the CM927 seems to be functioning perfectly well.
    All very confusing & frustrating!!
    Any help and advice would be greatly appreciated.
    Thanks
    Stephen
     

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