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Thread: Danfoss RAS C2 & HR91's

  1. #11
    Automated Home Lurker
    Join Date
    Dec 2020



    We recently had multiple new radiators fitted (with Danfoss RAS-C2 valves) and hit exactly the same issue. Not a single one of the radiators with HR91 units worked. The older HR80 units 'sort of' worked, but not on all radiators and not all the time.

    After talking with Evohome support, they confirmed that the HR91 (and HR-92 in default mode) do NOT fully open the valve to the end stop position and so would not work as I had them fitted.

    I did not want to switch out for HR92 units at significant expense, so I modified (bodged) the Evohome adaptors to work and added some basic instructions here for those brave enough to so a simple mod:

    I modified 6 HR91 adaptors and only broke one of them (10 replacement cost) and every one is now working perfectly. I wonder is there is a new manufacturing process on the Danfoss valves? Our plumber said they had used this combination before with no issues...

  2. #12
    Automated Home Legend
    Join Date
    Sep 2014


    Thanks for independently confirming that there is indeed a stroke compatibility issue with the HR91 with some valve bodies. As I mentioned in an earlier post I even had an issue with the HR91 not being compatible with the Peggler Bulldog which is a fairly standard (albeit cheap) M30x1.5 valve which "works" with the standard fitting that comes with the controllers. (No adaptor required)

    If you were able to file 0.5mm off and solve the problem when the total pin travel is about 3mm (4mm in stroke 1 mode on an HR92) it shows how close on the edge of working the pin offset is.

    Honeywell perhaps need to revise their Danfoss adaptor if new Danfoss valves have slightly different dimensions, to move the action point of the valve well into the operating range of the HR91/92 as you have done.

  3. #13
    Automated Home Lurker
    Join Date
    Dec 2020


    Some time has passed, but I've been meaning to update that I finally got my HR91s going! All it took was to change out the valves, again. To me at least there seems to be an issue with HR91 and Danfoss RAS C2 valves.

    I've spoken to Honeywell support (who very kindly also supported the valve switchover) and will be posting them some of my now spare valves so as they can test. Sounds like there has potentially been a design change somewhere along the line.

    Either way, a positive outcome. Thanks also to users on here who helped too.

    Now I just need to find that post with good starting points for programmes/setpoints... .

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