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Thread: Can an Evohome system be introduced in stages?

  1. #21
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    Now that I'm closer to placing an order that will include HR92 radiator controllers I need to know if they will fit my existing radiators. Most of them appear to have the required 30mm diameter connection (ref attached Radiator connector 1.jpg image) but five have very old Drayton TRVs that use a smaller connection of approx 26mm diameter (ref attached Radiator connector 2.jpg).

    What adapter is required to fit an HR92 to the latter connection? Does Honeywell supply such an adapter with each HR92?
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  2. #22
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  3. #23
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    Check if it's 26 or actually 28mm - I say this because I have a few TRV's that are 28mm, you can get a 28mm thingy for them instead of the more common 30mm doobries - I dunno what you call them, the bit that screws onto the TRV and has the black wheel and pin on the other end are available in both 28mm and 30mm sizes (I've got both). I've got a few Drayton TRV4's (30mm) in my house and they fit fine although I did have to use full stroke mode, your first image looks similar to a TRV4 but not exact, the second image you posted seems to have quite a short pin so normal stroke would probably be fine for that, only way to find out is to experiment really.

  4. #24
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    Quote Originally Posted by anniesboy View Post
    Thanks for that link, though it assumes you already know the correct name of your existing TRVs.

    Quote Originally Posted by therealfronty View Post
    Check if it's 26 or actually 28mm - I say this because I have a few TRV's that are 28mm, you can get a 28mm thingy for them instead of the more common 30mm doobries - I dunno what you call them, the bit that screws onto the TRV and has the black wheel and pin on the other end are available in both 28mm and 30mm sizes (I've got both). I've got a few Drayton TRV4's (30mm) in my house and they fit fine although I did have to use full stroke mode, your first image looks similar to a TRV4 but not exact, the second image you posted seems to have quite a short pin so normal stroke would probably be fine for that, only way to find out is to experiment really.
    Like you, I've no idea what you call the section of a TRV that has the pin and attaches to the radiator. The above compatibility chart covers 5 varieties of Drayton TRV. The 3 most recent models require no adapter and must therefore have 30mm connectors (unlike mine), while the older 2 are shown as not compatible - with no suitable adapter being listed. This suggests that I can't avoid having to drain my system to replace my Drayton TRVs with totally new valves.

    Since I don't fancy draining my system in the middle of winter when it's not essential, I'll choose to start by replacing some of the non-Drayton TRVs with HR92s.

  5. #25
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    We have a partial open plan layout in the ground floor of our house. As you can see in the attached diagram (which shows the radiators in magenta), there are no doors between our hall and kitchen and between the kitchen and dining room. There is also a large gap in the wall between the dining room and living room.

    Does this create a problem if I wished to designate the living room, dining room, kitchen and hall/WC as four separate Evohome zones?
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  6. #26
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    Quote Originally Posted by haggis999 View Post

    Like you, I've no idea what you call the section of a TRV that has the pin and attaches to the radiator.
    Honeywell refers to this as the `base plate`. Two versions exist, the standard 30mm that comes with the unit and a replacement 28mm version (ACH28). It must be noted here that I've never seen the 30mm as a replacement/service product, so if you are swapping valve bodies it appears wise to get yourself 28mm ones.

    Adapters exist for various other brands/types of valves and for Danfoss RA one is included in every box. If you get yourself the EU version you will in fact find two extra adapters in there: one for Caleffi and the second one appears to depend on date of production. The one I got had Danfoss RAV adapters and current ones appear to include the ACH28. You may not like the EU version though because the display is upside down (in continental Europe it is custom to have the valve mounted at the top of the radiator, whereas in UK it is usually at the bottom).

  7. #27
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    The very helpful guidance provided via this forum encouraged me to place an order yesterday for the Evohome controller, hot water kit and four HS92s. They are due for delivery tomorrow.

    In the meantime, I would be grateful for a response to my last post about creating zones in a partially open plan set of rooms.

  8. #28
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    Quote Originally Posted by haggis999 View Post
    We have a partial open plan layout in the ground floor of our house. As you can see in the attached diagram (which shows the radiators in magenta), there are no doors between our hall and kitchen and between the kitchen and dining room. There is also a large gap in the wall between the dining room and living room.

    Does this create a problem if I wished to designate the living room, dining room, kitchen and hall/WC as four separate Evohome zones?
    Well I have an open plan snug, conservatory and kitchen in a dog-leg design and have radiators in each room/area. They all work happily together and I occasionally turn dowen the snug radiator when not in use.

    I think you should set the rooms as you expect the temperature to be and monitor the actual rooms for performance against the set temps.

    The alternative is to set them all up as a multi room zone which may or may not use a tad more energy because you have removed the differential option to set different levels of temperature.

    An example for me is when my wife is baking tons of bread (don't ask) I might drop the kitchen setting a bit because there could be some decent heat coming out of the oven for hours at a time.

    Hope this might be of use to you.
    Last edited by killa47; 7th January 2022 at 09:09 AM.

  9. #29
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    That was going to be my initial approach. I'm glad to hear that it is a viable solution

  10. #30
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    Following the helpful guidance provided here a few days ago by gordonb3, I have now wired in a BDR91 to control the central heating. For the time being, I have defined a single zone that uses the thermostat in the Evohome central controller, which is located in our living room. I will add more zones when my HR92s are installed.

    The current setup now replaces what was being done by my ancient and unreadable CM207 controller.

    The first thing I have noticed about the new system is that if you request a substantial room temperature increase via the Evohome controller it takes several minutes before the BDR91 is activated. Similarly, it takes several minutes for the BDR91 to turn off after reducing the required temperature. Is this normal?

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