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Thread: Evohome - new installation advice and validation - advice appreciated

  1. #1
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    Default Evohome - new installation advice and validation - advice appreciated

    Hi all,

    My heating install is around 12 years old now, with a piped gas WB 40CDi driving what I have divined to be a pretty vanilla S-plan system, with two separate V4043H valves controlling hot water and heating, a mains-pressure, closed hot water system (i.e. no header tank) with a backup immersion heater and a conventional radiator setup (approx 13 radiators). A single (red) pump is used for moving water around the heating circuit, although there is also a separate bronze pump to feed a DHW circulation loop ensuring that there is always hot water close to the outlets. (I thought this a good idea at the time and my plumber fitted it - 12 years later, I'm still not sure it was a good idea or not!)

    I now work from home more often than not and am very aware that during the winter I am heating the whole house when, in fact, I rarely leave my office / kitchen. I thus started to look into various solutions for zone-based control and have settled on Evohome as having the best mix of features and (I hope!) longevity - after all, I'd rather not be replacing this every 3 years when it's suddenly made obsolete!

    My current plan is to purchase and install the following, which I think will suit my requirements:
    1 x Evohome wifi connected controller
    1 x BDR91 (heating control relay)
    13 x HR91 / HR92 TRVs
    1 x 10 way junction box
    1 x Hot water system (BDR91 + wireless temperature sensor)

    In the boiler room, I will replace the existing Honeywell 7-day clock and Honeywell "wiring centre" with a conventional 10-way junction box and pair of BDR91s. The new temperature sensor will be fitted to the tank, although this is actually only about 2ft from the boiler. Due to space, the two BDR91s were planned to sit next to each other, but I could probably separate them by 18 inches or so by putting one where the existing timer is, and the other below the immersion timer switch near the red pump (see photos). This will follow the "standard" S-plan wiring, with the BDR91s controlling the valves, and the valves controlling the boiler itself, more or less mimicing the existing wiring.

    Around the house, all radiators will get new TRVs (HR91 or HR92?) including the radiator in the hallway which currently has no TRV due to its proximity to the existing room thermostat. To ensure that a pumped water bypass path is still in place, the downstairs cloakroom radiator will have no TRV fitted and will be heated with latent heat from the demand created from the rest of the system. Should this prove problematic (i.e. turns the cloakroom into a sauna!), I will get a plumber to install a proper ABV loop instead and this room will get a manual TRV.

    This lot will be configured into 11 zones with only the kitchen containing multiple (3) radiators and the downstairs cloakroom having no smart TRV.

    If it's not already obvious, I'm not a plumber, but am reasonably confident that I can do the electrical side without a problem. (Put it this way, the existing wiring isn't exactly neat and I'm pretty sure I can do better than that!) Probably my biggest concern here is comms stability as my house consists mostly of brick internal walls and it'll be a reasonably distance from the kitchen (where I assume we'll keep the controller) to the loft room (the most distant radiator). I've also not decided yet whether to get HR91 or HR92 TRVs.

    I'm very interested to hear any feedback or suggestions of things I may have missed, or am doing completely wrong, ideally before I go ahead and spend lots of money!

    Some pics:

    Boiler and expansion vessels (shoes are sat on top of the hot water tank):
    20190902_155352.jpg

    Timer + valves (tank is to the left):
    20190902_155403.jpg

    Existing timer wiring:
    20190829_164742.jpg

    Proposed S-plan wiring:
    nReqvWH.jpg

  2. #2
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    I can't help you with the wiring as I got my evohome professionally installed, but here are my observations for what they're worth.

    If I was to start again, in the rooms with multiple TRVs that are in a zone, I would fit the cheaper HR91's and use a separate thermostat e.g. DTS92 or T87, for the temperature sensing/reading.

    You need some distance between your BDR91s and the hot water thermostat.

    Also swap out the valve bodies to Honeywell Valencia's so they work reliably with the TRVs.

    Do you have a separate towel rail circuit? I have a separate circuit for towel rails not fitted with HR9X's that gets heated water pumped around whenever the boiler comes on which is effectively the bypass.

  3. #3
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    Quote Originally Posted by Somebody View Post
    If I was to start again, in the rooms with multiple TRVs that are in a zone, I would fit the cheaper HR91's and use a separate thermostat e.g. DTS92 or T87, for the temperature sensing/reading.
    Yes, I'd already contemplated this using the T87 for the kitchen (the only room with multiple radiators). Seems a good solution and probably not much more expensive than using HR92s.

    Quote Originally Posted by Somebody View Post
    You need some distance between your BDR91s and the hot water thermostat.
    Hmmm, this ain't easy as the two are only going to be a 18" away maximum. No other way as the boiler, boiler controls and hot water tank are all in the same, relatively small room. What's the reason for this?

    Quote Originally Posted by Somebody View Post
    Also swap out the valve bodies to Honeywell Valencia's so they work reliably with the TRVs.
    Might be one for the future as, TBH, this makes the whole job a faff. I guess there's nothing precluding this if I have problems with th

    Quote Originally Posted by Somebody View Post
    Do you have a separate towel rail circuit? I have a separate circuit for towel rails not fitted with HR9X's that gets heated water pumped around whenever the boiler comes on which is effectively the bypass.
    No, the tower rad is just a normal radiator on the upstairs loop. It's currently without a TRV, so I'll add one in its own zone which can have more generous times to keep the towels dry. Maybe I'm as well leaving it as the upstairs towel rad. That's probably a question for my plumber to be fair...

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    Quote Originally Posted by daern View Post

    Hmmm, this ain't easy as the two are only going to be a 18" away maximum. No other way as the boiler, boiler controls and hot water tank are all in the same, relatively small room. What's the reason for this?
    Advice from page 3 of this guide:
    https://ensupport.getconnected.honey...ile_1__Body__s
    We therefore recommend that you:
    Mount the product at least 1 metre away from any other wireless device
    If you are mounting a pair of Honeywell products together, allow at least 1 metre gap between the two to avoid signal saturation

    You could mount one higher up the wall and the other beneath it, rather than side by side. This is how mine are installed, BDR91s on one wall, heating BDR91 high up, DHW low. The CS92 is on the adjacent wall.

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    Quote Originally Posted by Somebody View Post
    Advice from page 3 of this guide:
    https://ensupport.getconnected.honey...ile_1__Body__s
    We therefore recommend that you:
    Mount the product at least 1 metre away from any other wireless device
    If you are mounting a pair of Honeywell products together, allow at least 1 metre gap between the two to avoid signal saturation

    You could mount one higher up the wall and the other beneath it, rather than side by side. This is how mine are installed, BDR91s on one wall, heating BDR91 high up, DHW low. The CS92 is on the adjacent wall.
    Thanks, that's really useful. I will do some nosing around in the boiler room to see what I can do to separate them. It shouldn't be too much of a problem as only a single, 5-core wire is needed to be fed to the BDR91. Same goes for the CS92, which I can probably tuck away at the far side of the room.

  6. #6
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    BTW instead of using a radiator as a bypass I have an 'automatic bypass valve' which I think is better, unless you have an area you want to constantly heat.

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    Quote Originally Posted by Stevedh View Post
    BTW instead of using a radiator as a bypass I have an 'automatic bypass valve' which I think is better, unless you have an area you want to constantly heat.
    Thanks. I'd been considering that and was going to chat to my plumber about it when he comes back to finish my en-suite. The towel-rad bypass option mentioned above also isn't a daft idea.

  8. #8
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    You will have to leave the existing Dual cylinder/high limit stat wired in series with the EvoHome HW sensor/BDR91 to meet regs too.

    You've also already got an Automatic bypass in too, it's a requirement of Worcester and it's just before your motorised valves. Are you leaving the Motorised valves in?

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    Quote Originally Posted by mtmcgavock View Post
    You will have to leave the existing Dual cylinder/high limit stat wired in series with the EvoHome HW sensor/BDR91 to meet regs too.
    You'll have to excuse me - is this the existing stat that's in the cylinder? So I'd wire this in series with the HW BDR91, set with a high temperature set-point to ensure that the system can't ever go over temperature whatever crazy stuff the evohome says?

    Quote Originally Posted by mtmcgavock View Post
    You've also already got an Automatic bypass in too, it's a requirement of Worcester and it's just before your motorised valves. Are you leaving the Motorised valves in?
    Oh! This is news to me - I'll have another nose around at the pipework later then! Yes, I was assuming that the existing motorised valves would stay put and simply be controlled via the evohome rather than the existing Honeywell clock. Is there any reason to do otherwise?

  10. #10
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    Sorry for the delay in replying, Gmail decided to file the forum notification under spam.

    Quote Originally Posted by daern View Post
    You'll have to excuse me - is this the existing stat that's in the cylinder? So I'd wire this in series with the HW BDR91, set with a high temperature set-point to ensure that the system can't ever go over temperature whatever crazy stuff the evohome says?
    Yes this is the existing cylinder stat. Quite important this stays wired in and in use. As you say set it to it's highest set point, should EvoHome fail the cylinder stat will break the circuit, failing the that the high limit stat will click out breaking the circuit too.

    Quote Originally Posted by daern View Post
    Oh! This is news to me - I'll have another nose around at the pipework later then! Yes, I was assuming that the existing motorised valves would stay put and simply be controlled via the evohome rather than the existing Honeywell clock. Is there any reason to do otherwise?
    Yes that's fine, Honeywell suggest you remove these however in my own system I still have zone valves. What I would suggest though is you have a boiler relay as well though (Just another BDR91) that controls the boiler. This will allow you to have Hot Water over run then.

    Yes the automatic bypass is the red thing before the motorised valves on your pictures. All Worcesters require them, so it would be highly unusual for your system not to have one.

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