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Thread: Evohome without TRV's

  1. #1
    Automated Home Jr Member
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    Default Evohome without TRV's

    Hi,

    I just installed an Evohome and to delay the investment a bit I planned to not install TRV's in the living room (where the controller is installed).

    Since the controller can be used as temperature sensor and I can limit the room temperature by the existing standard TRV's this looked a great idea.

    When trying to configure this I however found out that in defining the zone you're forced to link a "device" (however I can click on connect and proceed).

    Having configured it this way the Evohome system doesn't activate my BDR91 for some reason ?

    Another option I figured out was to link the BDR91 both for heating control as well as a zone valve for the living room. This seems to work somehow (sometimes I have the feeling not but can't pinpoint it).

    Any other ideas on how to solve this ? (I can get another BDR91 from someone, maybe link that as dummy zone valve ?)

  2. #2
    Automated Home Ninja
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    Quote Originally Posted by DarkV View Post
    Any other ideas on how to solve this ? (I can get another BDR91 from someone, maybe link that as dummy zone valve ?)
    Fit two HR92s

  3. #3
    Automated Home Jr Member
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    Explain... why two ?

    Currently I've sacrificed another room to use one of the TRV's for the living room which works.

    Otherwise I need to buy an additional 7 ones for the entire living room.

  4. #4
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    If there are two radiators in the room you need one on each. As I understand it Evohome will not work as it should if you don’t fit a TRV to each radiator in the zone. An HR92 or its equivalent. The thermostat will tell the control panel heat is needed, the control panel will send out a signal to the HR92s to open up or close. If there are no HR92s on the radiators, unless you manually turn them down, they will get warm when another zone wants heat. Your thermostat in the lounge will then report too much heat there and the boiler goes off and your other room goes cold until the cycle starts again.

  5. #5
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    There is always a long debate about this (since some people seem to have found kludgy workarounds that work for them but not others) but the simple rule is this:

    A single zone system can be operated either relay only (replacing an existing thermostat in a room with no TRV) or with a TRV or some other "actuator".

    However as soon as you have more than one zone all zones with temperature sensors must have actuators bound to them.

    So you cannot have several zones with TRV's, then a zone with the Evotouch as the temperature sensor and no actuator (TRV or dedicated relay) in the zone. This is not supported, and I think the documentation is pretty clear on this.

    There are various tricks to try to get around this like double binding the boiler relay but having tried them myself in the early days where I was facing a similar situation with not enough HR92's to go around my advice is don't, you will have endless comms faults reported on the controller and things just won't work properly.

    Just buy another HR92 and be happy.
    Last edited by DBMandrake; 14th December 2020 at 10:17 AM.

  6. #6
    Automated Home Jr Member
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    Quote Originally Posted by DBMandrake View Post
    This is not supported, and I think the documentation is pretty clear on this.
    Do you have any reference to this ?

  7. #7
    Automated Home Guru
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    Quote Originally Posted by G4RHL View Post
    If there are two radiators in the room you need one on each. As I understand it Evohome will not work as it should if you don’t fit a TRV to each radiator in the zone. An HR92 or its equivalent. The thermostat will tell the control panel heat is needed, the control panel will send out a signal to the HR92s to open up or close. If there are no HR92s on the radiators, unless you manually turn them down, they will get warm when another zone wants heat. Your thermostat in the lounge will then report too much heat there and the boiler goes off and your other room goes cold until the cycle starts again.
    A single HR92 somewhere in a drawer will do the job just perfect. Obviously yes, if another zone requests heat then the `parasitic` radiators will heat up as well, but that may be perfectly okay for specific installations. Alternatively, in the case of a large number of radiators in a single zone you could consider installing a master valve.

  8. #8
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    I have a single HR92 installed now in the living room zone (contains 7 radiators) and this is fine for now.

    Since this is the biggest zone and always heated the "parasitic" behavior is not a real problem.

    In the long run I'll buy an additional 6 TRV's but this is quite an investment (the required piping changes for a zone valve, the valve and BRD91 won't save a lot).

    The reason for the topic is that it is unclear why a single HR92 makes this work (heat demand is regulated by the controller sensor anyway).

  9. #9
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    Quote Originally Posted by DarkV View Post
    I have a single HR92 installed now in the living room zone (contains 7 radiators) and this is fine for now.

    Since this is the biggest zone and always heated the "parasitic" behavior is not a real problem.

    In the long run I'll buy an additional 6 TRV's but this is quite an investment (the required piping changes for a zone valve, the valve and BRD91 won't save a lot).

    The reason for the topic is that it is unclear why a single HR92 makes this work (heat demand is regulated by the controller sensor anyway).
    As the HR92 is acting as an Actuator for the zone.

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