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Few Questions regarding Combi WMB-155c

JPL941 Member Posts: 50
Hello everyone. I have a few questions about my Weil Mclain WMB-155c.
I had an issue a little while back, now resolved, and the technician stated it was piped incorrectly. He stated he's installed many WMBs and knew right away it was wrong. I've also realized that it's been short cycling and I'd would like to redo all the piping.

At this point, I would like to add a buddy boiler 18 or buddy boiler 30 gallon tank (not much price difference from one to the other I found).

Looking at their install instructions I have a few questions:

1. Would you pipe it exactly the way they have it?
2. Currently I have an Amtrol #30, would I have to increase it to a #90 for the added water volume?
3. Should the piping make a loop or can it be separated as seen in the picture?
4. Is it appropriate to add a dirt separator with a magnet on the return side of the boiler?
5. The WMB-155c already has a built in circulator. I called WM today to see if it requires an additional circulator or could I get away with using the internal circulator. I really didn't get a straight answer. Thoughts?
6. Since the boiler Buddy is piped with black pipe, can I use mostly all black pipe? I saw there are black pipe manifolds etc, that I think would work well.

Thank you all for your time.


  • bob eck
    bob eck Member Posts: 929
    Before putting a boiler buddy on your system how many heating zones do you have? What type of system is it? Copper baseboard? Cast iron dashboard? Cast iron radiators? Duct coils? Steel radiant wall panels? Radiant?
    Is the outdoor reset control wired into the boiler control?
    If the outdoor reset control is wired into the boiler has the boiler control been set up?
  • hot_rod
    hot_rod Member Posts: 16,315
    Their manual indicates a separate circulator in the heating only boiler. The circ on board the combi should be plenty to give the minimum 6 gpm they require.

    How does the low output match your heating loads? Use any and all control options to limit short cycling first.

    If you do decide to buffer, I like a two pipe for that application. It gives you direct to load heating and also utilized the tank capacity best. That tank has large piping connections, should be a simple install.

    A multipurpose air/dirt/magnetic sep at the boiler supply to the tank.

    Here is a journal explaining the different piping methods.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • JPL941
    JPL941 Member Posts: 50
    Hello guys,

    Currently I only have two zones with two circulators.
    One zone is radiant flooring in our bathroom - I think the load is 5-6k btu. Using maybe 100-150 feet of 3/8" onix.

    The second zone is the kitchen running 1/2" pex to two toe kick heaters. Each heater is about 8/12k btu.

    It came with a reset controller but it wasn't installed because the plumber was concerned it may not get hot enough to trip the toe kick heaters.

    Who makes two pipe buffers? I'm only able to find 4 pipe.

    I do know it's oversized. My thought was if one of my steam radiators and or pipes were to leak, I would run pex to that room rather than tear the pipes out of the wall for repair.

    Thank you.
  • hot_rod
    hot_rod Member Posts: 16,315
    Sounds like you chose a 155 more for the DHW output?
    To make a 2 pipe buffer tank, plug all the ports you don't use on a 4 port tank :)

    If you can guesstimate total water capacity size expansion tank to that. Amtrol and Wessels have free online calculators.
    Easier sometimes to add a second 30 instead of replacing. a #60, or 2- #30 should be plenty.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream