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Check Valve Noise: Do I even need it ?

TAG Member Posts: 755
edited January 2021 in THE MAIN WALL

Now that my Viessmann has been up and running with all the radiant connected -- only noise heard is a slight in line check valve rattle on the secondary loop pump. The top one above the LLH. The system uses two pumps -- two identical Alpha II (the smaller size). Don't have the water to the building connected yet -- so the loop for the DHW is not operational (3 speed pump). These are the small valves that come with the pumps

Why would it be making noise and do I even need it ? How much ghost flow would I get w/o it? It's running with constant circulation and when the DHW would call the boiler loop pump to the LLH is off as well (with a cv) ?

The mechanical room is spaced challenged. Here is the system. Two of the four manifolds are in there and it shares the space with the generator control and all the electrical panels. This room is within the living space next to a bathroom .... I'm not sure anyone but me will ever even hear it.

I currently have both pumps on "auto" and the boiler loop seems to settle around 3/4 GPM .... the other pump is normally "HI". I have tried different settings for both (the picture shows it in III) .... the system pump needs to be in auto or III to keep the flow up.


  • BoilerToolbox
    BoilerToolbox Member Posts: 12
    I am assuming you are referring to the small plastic check valve that inserts into the pump flange? You shouldn't need it on the system loop pump. The low loss header is intended to provide a decoupling of the boiler loop and the system loop so that flow in one loop should not induce flow in the other loop. It is recommended that the boiler pump not be run in AUTO ADAPT. This mode is intended for loops that have changing states (i.e. zone valves opening and closing). The boiler loop does not change state, therefore you are better off to set the pump to a Constant Curve or Constant Pressure mode to ensure that you are meeting the boiler manufacturer's minimum flow rate.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,602
    I believe that @BoilerToolbox is correct about the check valve on that particular circ. I can't see any check valves either, so if it is the type inserted in the pump body or isolation valve, you can probably remove it.

    What will you check next after you remove the CV and you still have the noise? Since removing the CV is free, I would go for it. Just know that removing the CV is probably going to break it. That is my experience anyway.
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • TAG
    TAG Member Posts: 755
    Yes, the small check valve. Interesting -- on the boiler loop it seems to be always around 3/4 regardless of the setting. They say use middle setting for both constant curve and the pressure on a boiler loop .. but all the literature says you should be using "AUTO"

    Although thinking about it -- does the boiler always want exactly the same flow. Seems like maybe it does. Or does it maybe want lower flow when the output is lower?

    Right now I have everything wide open except some minor reduction to all the loops on the lower slab to limit some of the output to balance it all out. In the future there is a possibility of zones opening and closing when I get in the house. That's where I thought the constant pressure setting would be used -- But, Grundfos says still to use the AUTO. It will learn ?
  • BoilerToolbox
    BoilerToolbox Member Posts: 12
    Auto Adapt will learn your system over time and will be the best choice for your system pump. The boiler pump should be set to constant curve.