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Thread: Evohome - please help!

  1. #1
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    Default Evohome - please help!

    Hi everybody,

    Just had a new Vaillant Ecotek plus 637 system boiler installed with a Unistor unvented tank. I asked the installer to put in the Evohome controller (so the touchscreen and BDR91) and the hot water controller (BDR91 and the wireless thermostat). The system is set up with a common hot coming out of the boiler which is then allowed to the heating circuit via a Honeywell 2 port valve, and/or the hot water tank via a 2 way valve.

    The boiler fitter has left, he was not a specialist in Evohome. As he left it seemed to work but since I noticed that the calling for hot water caused the central heating to also come on. I have reset and rebound the BDR91s so many times now I am pulling my hair out. I just can't seem to get it where calling for hot water in the tank turns the boiler on and keeps the heating valve closed, it seems to open the valve but then doesn't turn on the heating, or in its current set up it does call for heat (the heating BDR91 turns on) but the heating valve also opens and again, I get heating without intending to.

    I will probably need to get him back but have I made a mistake in the settings in the Evohome which is leading to this behavior?

    Thank you so much!

  2. #2
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    I can't find the link to the setup instructions, but for your setup, don't go through the Evohome setup on the basis of using separate boiler and heating controls (BDR91's) reset and then add DHW and then follow the on-screen setup. If you are using the evohome Connected Thermostat Pack & evohome Hot Water Kit on an S Plan or Y Plan system (you are), you will not need a ‘Boiler Relay’ and this function must be ignored when you are asked the question when going through ‘ZONE GUIDED CONFIGURATION’ on the ‘INSTALLATION MENU’ of the evohome Controller!

  3. #3
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    Hi,
    Thanks for your help.

    So I have reset both the BDR91s and gone to the installation menu. I've got guided config, zone config, system devices, system parameters, add zone, system summary, RF comms check, factory reset. Which option should I be using please? I don't see any messages which use the term "boiler relay". Has the menu layout changed because I have seen reference to "boiler relay" elsewhere but don't see it on mine. I will try to keep googling.

    Thanks

  4. #4
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    I have figured out what you meant now and it is so blooming obvious! When you go to the heat section it asks you to bind the wireless thermostat, then the hot water BDR and then the heating BDR. As somebody that didn't read it properly I was binding the hot water one twice.

    Now the valves are controlled properly but the hot water option does not activate the boiler, this might be a valve wiring issue I guess. Off to look.

  5. #5
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    A rhetorical question: 'why do installers readily agree to install something that is outwith their experience and competency'?

  6. #6
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    Quote Originally Posted by Paulharr View Post
    I have figured out what you meant now and it is so blooming obvious! When you go to the heat section it asks you to bind the wireless thermostat, then the hot water BDR and then the heating BDR. As somebody that didn't read it properly I was binding the hot water one twice.

    Now the valves are controlled properly but the hot water option does not activate the boiler, this might be a valve wiring issue I guess. Off to look.
    If you don't have a BDR controlling your boiler, then the boiler is presumably controlled using the traditional orange wire from the microswitches in the valves. So, yes, I would guess this is a valve wiring issue.

  7. #7
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    Quote Originally Posted by dty View Post
    If you don't have a BDR controlling your boiler, then the boiler is presumably controlled using the traditional orange wire from the microswitches in the valves. So, yes, I would guess this is a valve wiring issue.
    Yes, sounds like the orange wire for the heating zone valve is connected to fire the boiler but the one from the hot water zone valve isn't - both need to be able to fire the boiler.

  8. #8
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    Cheers guys, turns out I was right and wrong. The orange wire from the valve wasn't getting live but that's because the overheat stat on the tank was stopping it. This is because whilst the Honeywell thermocouple in the thermowell of the tank was reporting low temperatures, the tank was actually hot. I will need to improve the Honeywell thermocouple.

    I am a chemical engineer so this type of thing is fun for me, but I can imagine that the average member of the public would not want this hassle to get hot water and heating!

    Next job, balancing 23 radiators until I can afford to buy 23 evohome TRVs!

    Any other good advice on this system? When I replace my bathrooms I will install electric underfloor heating in these and have these connected to the Evohome (based on advice already from here instead of a wet system).

    THanks again guys.

  9. #9
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    Quote Originally Posted by Paulharr View Post
    Cheers guys, turns out I was right and wrong. The orange wire from the valve wasn't getting live but that's because the overheat stat on the tank was stopping it. This is because whilst the Honeywell thermocouple in the thermowell of the tank was reporting low temperatures, the tank was actually hot. I will need to improve the Honeywell thermocouple.

    I am a chemical engineer so this type of thing is fun for me, but I can imagine that the average member of the public would not want this hassle to get hot water and heating!

    Next job, balancing 23 radiators until I can afford to buy 23 evohome TRVs!

    Any other good advice on this system? When I replace my bathrooms I will install electric underfloor heating in these and have these connected to the Evohome (based on advice already from here instead of a wet system).

    THanks again guys.
    Great you got it sorted can you tell me please how you intend to connect electric underfloor heating to Evohome

    thx

  10. #10
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    Quote Originally Posted by Paulharr View Post
    Cheers guys, turns out I was right and wrong. The orange wire from the valve wasn't getting live but that's because the overheat stat on the tank was stopping it. This is because whilst the Honeywell thermocouple in the thermowell of the tank was reporting low temperatures, the tank was actually hot. I will need to improve the Honeywell thermocouple.
    .
    I have a 17 year old Oso unvented cylinder and I have used the HW kit now for over 3 years with just the occasional sensor comms fault. The sensor is placed about a 1/3 of the way up the cylinder and to comply with the appropriate regulations it is wired in series with the cylinder thermostat - with the tank then protected by the Safety Stat. The key to getting it to work properly is to the adjust the normal unvented temperature stat to a slightly higher temperature than the one that is set in Evohome. It follows that if the HW kit fails, then the normal stat will kick in. In the unlikely event of both controlling stats failing, then the Safety Stat (86C in the case of Oso) protects the cylinder from an overheat situation.

    My thermocouple has just been pushed up against the cylinder under the foam insulation: nothing as fancy as a thermowell on the Oso.

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