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Thread: Danfoss RAS C2 & HR91's

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    Default Danfoss RAS C2 & HR91's

    New to the forum - long time lurker whilst I gathered advice & finally took he plunge last week for an Evohome setup.

    Install has gone smoothly & all set up, however having one issue with the HR91 heads where the trvs don't seem to open fully (all Danfoss RAs C2's) meaning very little heat is coming through (if at all). When I remove the head, the rotating assembly can be unscrewed 1 turn, which then fully opens the valve & water can be heard flowing. WHen I replace it, I can hear it do the calibrate thing, but the problem persists.

    Anyone had anything similar or have any advice/thoughts?

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    I actually installed this combination late this evening. I think it is working, but need more time to confirm.

    One question. The instruction suggests installing a plastic pin that comes with the HR91. Did you do this? It just didn't seem right to me and I've left it out initially.

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    Quote Originally Posted by lloyd View Post
    I actually installed this combination late this evening. I think it is working, but need more time to confirm.

    One question. The instruction suggests installing a plastic pin that comes with the HR91. Did you do this? It just didn't seem right to me and I've left it out initially.
    Be interested to know how you get on. When the system status showed 100% in a zone the radiator definitely wasn't hot, also checked another rad which isn't zone controlled and it was definitely hot!

    I didn't use the plastic pin, just didn't seem to fit as per the instructions.....

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    So it does seem to be working fine. One test you could try would be to use the override function and listen to now much it turns. You could also remove the head with it in fully on and fully off positions and see where the black wheel is.

    I did find this support article which describes correct positioning of adaptor, but if you had this wrong I think it would show the opposite effect to that which you are seeing.

    (I believe from pictures that I have an RAS C2, but should point out that a I can't confirm it.)

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    Issues still persist unfortunately. So when the valves show as fully open on systems status (100%) and I remove the hr91 head, there is a full turn available for the black disc to be unwound. As I turn it I can then hear water flowing through the rad.

    Is this normal? Is it something it will calibrate itself over time? An I able to set pin position or calibrate it manually?

    Right now I've got all heads removed and the radiators open to just get some heat into the house!

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    Quote Originally Posted by s.w.webb1 View Post
    Issues still persist unfortunately. So when the valves show as fully open on systems status (100%) and I remove the hr91 head, there is a full turn available for the black disc to be unwound. As I turn it I can then hear water flowing through the rad.

    Is this normal? Is it something it will calibrate itself over time? An I able to set pin position or calibrate it manually?

    Right now I've got all heads removed and the radiators open to just get some heat into the house!
    Probably not what you want to hear but...

    I trialled an HR91 on my system (which already had HR92's) when they first came out and I did not find the HR91 compatible with the valve bodies that I had at the time. (Pegler Bulldog - I now have Honeywell Valencia, but I sent the HR91 back before I changed valve bodies)

    The gearing of the motor on the HR91's seems to be less geared down compared to an HR92 (they move the pin faster from end to end but with less force) and they do not have the Stroke 0/1 configuration option of the HR92 which is a crucial omission when it comes to ensuring broad compatibility with different valve bodies.

    On an HR92 it's also normal for there to be about 1 full turn of the black wheel still available when the HR92 reports it is fully open - in the default Stroke 0 mode. This is normally plenty for most valve bodies as it's typical for a valve body to only have about 3mm of usable pin travel between fully pushed down and fully up. However some valve bodies have a bit more travel - about 4mm.

    On an HR92 you can change stroke mode to 1 and this applies more force when closing the valve but also expands the working range so that it turns the black wheel fully anti-clockwise right to the limit stop in the 100% open configuration.

    This may be necessary on some valves that don't fully flow until the pin is more or less right at the top - which is what I found with the Pegler Bulldog valves. They simply wouldn't let the radiator heat fully on some of my radiators until I changed the HR92 to Stroke 1 mode, and this got worse as the valve bodies got older and more "sticky" in their operation.

    Unfortunately the HR91 has no Stroke setting and seems to behave similarly to the Stroke 0 setting on the HR92 in terms of pin travel, so if it doesn't move the pin far enough I'm afraid you're stuck. I would be wary of recommending the HR91 for use with non Honeywell valve bodies due to the lack of the Stroke configuration option, and I reported as much on this forum back at that time when I sent the HR91 back. (A couple of years ago now)

    I would say your only choices would be to either swap all the valve bodies and cross your fingers for better compatibility, or swap the HR91's for HR92's in Stroke 1 mode. Perhaps get one HR92 first and do some testing with it in both Stroke 0 and 1 modes.

    Just my person opinion but I don't think the cost saving of the HR91 is warranted against the reduced functionality and compatibility vs the HR92. It's not just screen vs no screen, there are several configuration options like Stroke available in the HR92 which are absent in the HR91.
    Last edited by DBMandrake; 4th December 2020 at 10:31 AM.

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    This implies your valves are compatible but are ?

    https://theevohomeshop.co.uk/content...-compatibility

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    Quote Originally Posted by anniesboy View Post
    This implies your valves are compatible but are ?

    https://theevohomeshop.co.uk/content...-compatibility
    Depends what you mean by compatible.

    The fitting screws on and sort of works? Sure.

    Works properly and moves the pin across the full range the valve needs and controls the radiator effectively and has been thoroughly tested? Maybe. Compatibility is not just a binary thing unfortunately.

    I see the Peggler Bulldog is on that compatible list as well, and while they are standard M30 x 1.5 threads with a standard pin height and worked "OK" for me for a while in the end I had trouble with them in less than 2 years and had to resort to Stroke 1 mode to get them working acceptably and even then I had enough hassles with them that I opted to replace them at considerable cost with the Honeywell Valencia.

    That list was probably originally made with the HR92 in mind with an assumption that valve bodies an HR92 fits must work with the HR91 as well. However the motor actuator of the HR91 is different to the HR92 and it doesn't have both stroke modes available.

    Very small differences in the pin height, pin travel and the type of rubber gasket inside the valve body (which affects how hard the HR91/HR92 has to push to get a seal and how far the gasket compresses) as well as the strength of the return spring in the valve can have quite a large effect on how well the radiator is actually controlled, as the heat demand sent wirelessly to the boiler is inextricably linked to the valve pin position - so if your valve pin needs to be unusually low or unusually high to get the right operating point, it won't work well as the heat demand sent will be out of whack with the water flow through the radiator.

    This is not a problem traditional wax pellet radiator controllers have because they just control the radiator and don't send an electronic heat demand. Also the HR92 has a range of only 4mm total travel which is non-adjustable for offset, while with a wax pellet controller turning the knob actually moves the wax capsule up and down on top of the pin so they have a large compensation range available for variations in pin height between valve bodies. (Also the controllers usually come matched with the valve bodies anyway so are designed explicitly to work well with each other)
    Last edited by DBMandrake; 4th December 2020 at 12:36 PM.

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    Thanks for the replies everyone. Some good intel I here. Unfortunately for me I'm still no further ahead. Have had a bit of back and forth with Honeywell tech support, nothing glaringly wrong on the install side yet.....

    My issue is if I was to upgrade to HR92s then I'm likely stuck with 10 HR91s that are of no use to me and which Im unlikely to be able to return (been unboxed/fitted etc). So .

    My other get out is new valves. Again. The danfoss ones were fitted for this purpose, so it won't come cheap, but it would be cheaper than HR92s. If this does come about - what valves are 100% compatible with HR91s so I can guarantee I won't hit the same issue again? Honeywell Valencia's?

    https://www.screwfix.com/p/honeywell...questid=353169

    Many thanks for your wisdom!

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    Quote Originally Posted by s.w.webb1 View Post
    Thanks for the replies everyone. Some good intel I here. Unfortunately for me I'm still no further ahead. Have had a bit of back and forth with Honeywell tech support, nothing glaringly wrong on the install side yet.....

    My issue is if I was to upgrade to HR92s then I'm likely stuck with 10 HR91s that are of no use to me and which Im unlikely to be able to return (been unboxed/fitted etc). So .

    My other get out is new valves. Again. The danfoss ones were fitted for this purpose, so it won't come cheap, but it would be cheaper than HR92s. If this does come about - what valves are 100% compatible with HR91s so I can guarantee I won't hit the same issue again? Honeywell Valencia's?

    https://www.screwfix.com/p/honeywell...questid=353169

    Many thanks for your wisdom!
    I must admit that I am surprised that your experience is so bad. If the head does not have enough torque or throw to close the valve, then you would have the opposite issue. I suppose the question is why does there appear to be a turn left on the wheel when the valve should be open? Do you actually here the head trying to calibrate?

    I know that HR91 has less options to fiddle with than the HR92, but I would expect you to get a better experience than you are getting, if not perfect. As I've said in a previous post, I have one RAS-C2 with a HR91, and that works fine.

    When I installed my system I had some stuck and some incompatible valves, and I replaced these with Valencias. They work fine (but so does the RAS-C2 !)

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