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Buderus Panel Radiator Flow Setter Valves

pyme66 Member Posts: 4
In my hydronic system I installed two years ago, I have a zone with Buderus panel radiators. The zone has a two pipe reverse return configuration. Everything run fine the first winter, but this year I have three panels (out of 8 panels in the zone) that have flow setter valves (see attached image for velvet) that are frozen shut. The panels in question get no flow. I went through the usual troubleshooting routine checking air bleeding, isolation valves, etc. are narrowed it down to the flow setter valves. I have removed the Danfoss sensor heads and can see some oxidation around the stem of the valves. I also tried Kroil penetrating oil on the stem while tapping on the valve body, no luck so far.
Does anyone have experience with servicing these valves? I have information about how to remove them and clean them.
Thanks in advance.


  • Ironman
    Ironman Member Posts: 6,868
    You'll probably have to replace them, but they are symptomatic of a larger problem: system leaks which cause fresh water and minerals to be constantly added. Find and fix your leaks.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • pyme66
    pyme66 Member Posts: 4
    I don't have any leaks in the system. Since initial install, I had to replace the zone valve (in the same zone), a process that added a small amount of fresh water since the zone valve can be isolated.
    The one possible issue is that the makeup water is coming from the water softener line, I am unsure whether is acceptable in a hydronic system.

    For now I was able to recover from the problem. The valve stems/pins are sealed with a small O-ring. Some oxidation around the O-ring prevented the pins from moving freely. One of them release a day after penetrating oil was applied. I was able to release the other two by lightly pulling them straight out with pliers. The system is back to working normally. There does not seem to be a problem with the valves themselves.

    For the long term, two questions remain: (1) is softener treated water permissible? (2) would adding antifreeze (boiler manufacturer recommends CRYO-TEK 100) help with oxidation?

    Thanks for any help.
  • Ironman
    Ironman Member Posts: 6,868
    No on both questions. You should flush the softened water out and refill with fresh water. Check your ph level to make sure it's within manufacturer's specs.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 3,201
    I like reason for the answers, Antifreeze in the water will change the Specific Gravity of the heat transfer solution. If the radiators are properly sized then you will make them somewhat smaller with antifreeze. (Smaller capacity... not physically smaller). To compensate the boiler water will need to get hotter. (only on the coldest days). Also, if there are any leaks, antifreeze will just make the leaks messier! (more messy)


    Treated water from your softener may have chemicals in there that you don't want in the boiler Test the untreated water for Ph and iron content. Use that water to fill the boiler and then add the proper boiler water treatment to that water. Once the boiler water is in there for a few days, it will become inert and as long as you don't add any more water your system will balance out (chemically) and the corrosion will be minimized.

    Close the manual feed valve after the system is stabilized (pressure). then see if the pressure drops over time. if it does, you have a small leak. as the leak(s) let water out, the auto feed was letting water in. Adding to your problem.

    Edward Young
    Retired HVAC Contractor from So. Jersey.
    Services first oil burner at age 16
    P/T trainer for EH-CC.org