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Thread: Evo S Plan

  1. #1
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    Default Evo S Plan

    Weve recently had a new heating system installed. The boiler is an external wall mounted Grant Vortex Eco. The system was plumbed S plan using 2 Honeywell V4043H1056 zone valves.

    The Evo components are the Wireless Connected Control Pack (AC928 & BDR91) and the Hot Water Kit (CS292 & BDR91) . All except 2 small radiators (porch and bathroom which I was content to allow to come on with any CH demand) are fitted with HR80 or HR92 (a mix).

    The electricians who were unfamiliar with the Evo system had problems. While all the Radiator valves were communicating with the Central Controller, a call for CH did not turn on the BDR91 for CH. There was also a strange condition where the green lights on both BDR91s were off but the boiler and pump ran and the CH valve stayed open.

    They left the job at this stage and apparently consulted Honeywell before returning. They have since made two visible changes. One was to move one of the relays they fitted I guess this is just for reasons of signal they were only about 5cm apart before. The other is that they have disconnected the CH zone vale and locked it open. The BRD91s now seem to work #1 to control the boiler and #2 to open the zone valve on the HW circuit. Im not over happy with this as the 2 small rads come on with both CH and HW demands.

    The only comment I picked up was something about the zone valves being incompatible with the S Plan but I cant figure that out as the S Plan wiring diagram in the Evo installation manual shows 2 x V4043H. The only difference Ive spotted between what we have and that diagram is that our boiler needs a permanent live.

    Can someone advise me. Is it impossible to have our system using S Plan or what components would need changing to achieve this?

  2. #2
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    It's absolutely possible to have an S plan configuration for the Evohome. Depending on how you intend to fire the boiler, you will have 3 x BDR91s. 1 as a Boiler Relay and the other 2 controlling the CH and HW motorised valves. Locking open the CH valve is done only when all radiators have radiator valves attached to them, making a motorised valve redundant. That is why your radiators are getting hot when there is HW demand only. Now again depending on your preference you might want a radiator (e.g. towel rail) to come on with any demand.

  3. #3
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    Quote Originally Posted by bruce_miranda View Post
    It's absolutely possible to have an S plan configuration for the Evohome. Depending on how you intend to fire the boiler, you will have 3 x BDR91s. 1 as a Boiler Relay and the other 2 controlling the CH and HW motorised valves. Locking open the CH valve is done only when all radiators have radiator valves attached to them, making a motorised valve redundant. That is why your radiators are getting hot when there is HW demand only. Now again depending on your preference you might want a radiator (e.g. towel rail) to come on with any demand.
    If you weren't wanting to purchase another relay you can just use the two relays that you have got, one to control the heating valve and one to control the HW valve. You then use the S/L from the motorised valves to fire the boiler. This was how I set mine up to start with and then added a boiler relay at a later date.

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    Thanks both. I was hoping there was a 2 x BDR91 way. What is the advantage of a third?

    There again, it might be an idea for me to think more on the purpose of the small radiator in the bathroom before actually making changes. As things stand, the porch radiator would need an HR92 but bruce_miranda might have a point - I'd not considered it before but it might actually be desirable to have the bathroom one on with any demand...

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    Quote Originally Posted by jonbanjo View Post
    Thanks both. I was hoping there was a 2 x BDR91 way.
    There is a 2 x BDR91 way, as mtmcgavock said. You have the BDRs effectively acting like the two sides of a conventional controller and opening the valves. All other wiring remains "conventional". In particular, the two orange wires (the switched lives) from the valves are used to fire the boiler.

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    Quote Originally Posted by jonbanjo View Post
    Thanks both. I was hoping there was a 2 x BDR91 way. What is the advantage of a third?

    There again, it might be an idea for me to think more on the purpose of the small radiator in the bathroom before actually making changes. As things stand, the porch radiator would need an HR92 but bruce_miranda might have a point - I'd not considered it before but it might actually be desirable to have the bathroom one on with any demand...
    The main advantage with the third is that you can utilise the Hot water overrun features. So once you HW is heated up the boiler will stop firing and leave the HW motorised valve open for a set period of time to disperse the heat from the boiler. Also it will allow you to configure the boiler minimum on time (Although the parents have the two BDR91 set up and they're cycle/min on time seems to work ).

    Regarding having the bathroom radiator on with any demand - it may get rather hot in there. I have my towel rails on with just the HW (I wired it so I can switch this on and off) and depending on your hot water usage and recovery time it can get rather hot in the room. My best suggestion would be to have HR92s on all the rads therefore in summer if you just want the bathroom rad on you can switch it on.

  7. #7
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    If you have S-Plan take a look at Simon (DBMandrake)'s alternative wiring scheme - it has definite advantages over the setup in the Honeywell manual.

    P.

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    Speaking of which, another 2 x BDR91 solution is to use 1 as the boiler relay, the other as the HW valve relay but then wire your CH Valve to open with the boiler pump. This was again something that Simon (DBMandrake) came up with and works very well in my house. It makes the system act like having no valve on the CH side and yet has the valve operational and fully open when needed. Then during pump over runs there is a longer length of pipe for the water to dissipate heat across rather than just the bypass valve. Also you have a few non HRxx radiators too.
    Another way I have seen it being done is to run a single BDR91 as a HW priority system. But then the disadvantage is that you are still powering the CH Valve when the heating is Off.

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    Quote Originally Posted by dty View Post
    There is a 2 x BDR91 way, as mtmcgavock said. You have the BDRs effectively acting like the two sides of a conventional controller and opening the valves. All other wiring remains "conventional". In particular, the two orange wires (the switched lives) from the valves are used to fire the boiler.
    This is how I had it wired for the longest time before I went OT. Infact I had the 2 channel time clock wired in parallel too, this allowed my wife some transition time to Evohome.

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    Thanks again. I guess I should have tried more of my own reading first but my starting point was was what the tradesmen told me I think Im starting to get a better picture of how Evohome works and at least a few of the different configurations possible. (I installed our previous controls Older Honeywell with CM67z and HR** for CH and Danfoss for HW but with a new system installed, decided the time to give up DIY heating up and leave it to the pros. It does seem though that I still need and/or desire some degree of understanding of the Evohome system).

    Im not sure whether I should continue with this one here but my reading has led me to worry about something else. As far as I can make out, they have simply removed the combined temperature/ thermal cut out unit from the CenterStore unvented cylinder and replaced it with the Honeywell probe. Im getting the impression this is not a good idea?

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