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Worcester HE R35 Wiring for Room Thermostat

Discussion in 'Plumbing and Central Heating' started by tffitch, 20 Nov 2009.

  1. tffitch

    tffitch

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    I have just ordered a Honeywell CM927 Wireless Programmable Room Thermostat for my Worcester Greenstar HE R35 combi boiler. This is an older model boiler from about 7 years ago.

    The CM927 wiring diagram shows 2 connections from the stat to the boiler, at the stat end the A terminal goes to T1 on the bolier and B on the stat to T2 on the bolier.

    Looking at the wiring diagram for Bosch's own room thermostat for this bolier there are 3 connections, labelled F, 3 and 4 at both the boiler and stat end.

    Can anyone tell me how I should wire up the CM927 to this boiler. There is no room thermostat fitted at present.

    Thank you
    Tim.
     
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  3. jackthom

    jackthom

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    On the boiler connector 328 (where the mains enters the main PCB), there will be a wire link at the moment between Ls and Lr.

    Remove the link and

    connect Ls to A on the 927

    connect Lr to B on the 927

    Connect up Live and Neutral as per diagram.
     
  4. tffitch

    tffitch

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    Thanks for your reply. I rang Worcester Bosch technical support earlier who said this model boiler will only work with their own thermostat. This was rectified with later models.

    The model I have is Greenstar HE Plus R35. Does what you suggest apply to this model or later model.

    Thanks
    Tim
     
  5. bengasman

    bengasman

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    I have never seen a WB that did not work on a universal stat, but I have not seen every WB ever made.
    Post the GC number if you want to be sure.
     
  6. jackthom

    jackthom

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    As bengasman says it would be unusual.

    Assuming you find the wire link in the boiler and removing it prevents the CH from working I can't see how the 927 can fail to work.

    To be on the safe side DON'T connect LIVE to terminal A in the 927 and then it will be operating as a simple switch, just like the wire link did.
     
  7. OldGeezer

    OldGeezer

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    The Worcester TR2 thermostat used with this boiler was looking a bit dated so I decided to replace it with a Honeywell CM927.
    The TR2 is just a set of selectable resistors and a thermistor (temperature sensitive resistor.)
    On the boiler (WITH IT POWERED OFF) , I connected a 3.3K resistor between terminals 4 and F - (this fools the boiler into thinking the room temperature is about 11 degrees C). I then connected a 10K resistor in series with a 2.2K resistor between terminals 3 and 4 (Total resistance 12.2K). This makes the boiler only operate in frost protection mode only.
    I then connected the A and B terminals from the CM927 to either side of the 2.2K resistor.
    So that when there is a demand for heat this resistor is shorted and the resistance between terminals 3 and 4 drops to 10K. This causes the boiler to think the requested temperature is now about 18 degrees and as it thinks the room temperature is 11 degrees it fires up

    So if you have some experience of electronics or a friend who does, this may be a way of updating the controls on this boiler. Of course I can't except any responsibility!
     
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  8. Aidan1066

    Aidan1066

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    Thanks OldGeezer, i did your trick with the resistors on a HE40 and am now successfully using a Towerstat RF voltfree programmable thermostat instead of the tr2 that went faulty on me after moving into my new house recently. I didn't like the TR2 anyway as there is no indication (no click or led) showing whether it is calling for heat.

    Incidentally my TR2 had been installed about 2 inches away from a corner in the hall so was never going to work well and the installer had used a bare earth conductor on 1mm twin & earth cable as one of the live signal conductors - not impressed.

    Anyway, thanks very much to you for that very useful info.

    Aidan :D
     
  9. Ginger81

    Ginger81

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    Hi All,

    I'm aware this is an old post but there might be some survivors out there. ...

    I have the same problem on this TR2 thermostat controller. I am trying to install a hive heating thermostat. I have completed the wiring diagram as above making sure that the resistor switches from 12.2 ohms to 10 ohms when the hive commands the heating to be on. And back again to 12.2 when there is no demand for heating. I plugged this in and all appears to be well room temperature is set at 11.5°C and in frost protection mode.

    I then give the hive a command from heat and the target temperature of the room moves to 18.5°C and the boiler fires up in comfort on mode. All appears to be working. Then…

    I give the hive are stop heating command and I hear they're relay click inside heat link however the boiler is now stuck on 18.5°C target temperature and still in comfort on mode it does not go back into frost protection mode.

    It is stuck in manual mode with comfort on.

    Any suggestions why this is??
     
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  11. picasso

    picasso

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  12. Ginger81

    Ginger81

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    Thanks Picasso,

    I'll try this and let you know.

    Cheers
     
  13. goodtruth

    goodtruth

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    Thanks OldGeezer... legend!

    Ginger81, did the adjustment of the 'set economy temp' work for you? (Thanks to you too Picasso.)

    Could anyone post a pic of the wire up please?

    Am I right in assuming that the power to the new thermostat (receiver for wireless) does not come from the boiler then?


    Thanks in advance.
     
  14. Ginger81

    Ginger81

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    Goodtruth, I have only just managed to get this working however this has been many a try that’s failed. I’m hoping this is the solution.

    You need to leave the original TR2 connected and use the new switch in conjunction with a resistor in parallel to fool the Boiler target temp.

    When I’ve got time I’ll post a solution.
     
  15. goodtruth

    goodtruth

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    Thanks Ginger81.

    That has completely thrown me because I dont even have a TR2 and was banking on fooling the boiler!

    I'll wait for your post and thanks again.
     
  16. LeeB2

    LeeB2

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    Hi all,
    Had a BG engineer try and fit a Hive to me WB greenstar r35 he to no avail. Considering the post above using resistance control to set the input to work with Volt free with everyone using Honeywell CM927, can i assume this would then work with any Volt free wireless thermostat? eg Hive, Nest?

    Cheers to anyone still following this thread. Lee
     
  17. grnunn

    grnunn

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