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Thread: Bind Unconnected HR92

  1. #1
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    Default Bind Unconnected HR92

    I recently purchased Evohome for all the radiators in my house plus a hot water control.

    However, while I thought I might be able to self install the wiring was too much for me and all my radiators require new valves fitted.

    I have arranged an electrican to do all the electrical work and separately going to get a plumber to replace the valves.

    The electrican will be here a couple of weeks before the plumber (Christmas schedules!)

    Wondering if I can bind a HR92 that isnt connected to a radiator and use that to control the boiler if it is bound through the control.

    I accept I will have no control over heating in other rooms apart from existing TRVs just wondering if it is possible to do?

  2. #2
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    If you put the bottom half of the HR92 on the top it fools the radiator valve to think that it is connected to the radiator. Then you can fire the boiler with a single HR92 like a manual switch.

  3. #3
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    Quote Originally Posted by bruce_miranda View Post
    If you put the bottom half of the HR92 on the top it fools the radiator valve to think that it is connected to the radiator. Then you can fire the boiler with a single HR92 like a manual switch.
    Yes - just make sure the little latch that locks it onto the wheel unit is latched as well, otherwise it won't call for heat.

    Then sit the HR92 in the room where you want to measure the temperature on a small table. Or you could configure the Evotouch controller to be the temperature sensor for that zone, then the HR92 just become a "dummy" actuator that will fool the system into working.

    Yet another option is you could just set up the system in single zone mode where it doesn't expect there to be any HR92's - in that mode the Evotouch controller is the temperature sensor for the "whole house" just like a conventional thermostat and will fire the boiler via the BDR91. This emulates a traditional single thermostat.

    I think you can use this single zone, no HR92's mode of operation with stored hot water as well (two BDR91) although I haven't tried that.

    When you get your valves changed over you would need to reconfigure the controller from scratch for the new setup with HR92's, but that's not hard.
    Last edited by DBMandrake; 13th December 2017 at 12:12 PM.

  4. #4
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    Thanks for that went with using the Evohome controller as the single thermostat for the house.

    One other question. I have bound the hot water temperature sensor and a BDR91 to the hot water cylinder and seems to be connected and bound correctly but the immersion heater doesn't appear to be coming on. Does this setup make sense?

  5. #5
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    Are you trying to drive the immersion heater directly via the BDR91? The BDR91 isn't rated for an immersion. The BDR91 should fire the boiler which heats the HW cylinder. The immersion should be on its on separate switch.

  6. #6
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    Quote Originally Posted by bruce_miranda View Post
    Are you trying to drive the immersion heater directly via the BDR91? The BDR91 isn't rated for an immersion. The BDR91 should fire the boiler which heats the HW cylinder. The immersion should be on its on separate switch.
    Indeed, a BDR91 is only rated for 5 amps, or about 1200 watts. Have a look inside the BDR91 - the relay is tiny, as are the terminals. A small immersion element is about 3kW and a big one is up to 6kW, so both are well outside the relays rating so will probably do serious damage to the BDR91's relay in fairly short time, assuming there isn't a fuse in there that will blow first. (I don't remember seeing a fuse!)

    Evohome is not really designed to control electric hot water elements. In theory it might work if you drove another larger suitably rated contactor/relay using the hot water BDR91, but you would only be able to use a 2 BDR91 configuration (hot water relay and heating relay) as a 3rd boiler control relay would be fired when there is hot water demand.

    Do you have an S-Plan system or is your hot water immersion heating only ?

  7. #7
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    I have a Y plan system with just hot water on or hot water and heating. I currently have a manual valve beside the boiler where I can switch between these two.
    Could I replace the manual valve with one compatible with Evohome?

    I thought the BDR91 would turn the switch on the wall to turn the heating on and off but obviously not how it works.

    IMG_20171213_224229119.jpg
    Last edited by lorcanjc; 13th December 2017 at 11:53 PM.

  8. #8
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    So no timer? I think you need to get an electrician in. Giving you advice based on that photo is likely to be incorrect. I cannot tell whether those switches are for the immersion or for the boiler etc.

  9. #9
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    Quote Originally Posted by bruce_miranda View Post
    So no timer? I think you need to get an electrician in. Giving you advice based on that photo is likely to be incorrect. I cannot tell whether those switches are for the immersion or for the boiler etc.
    It was an electrican who fitted it for me

    The switch and fuse and both for the immersion. I think the electrican just replaced the old time clock in the circuit with the BDR91

  10. #10
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    Call him back.

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