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As @bjohnhy mentioned, at low flow it could be a check valve rattling. However with a zone valve system, you don't need the check valve installed anyway.

You have lots of zones and I am sure it starts to settle down at the 9 watt range which is the slowest speed the circ runs at and could cause a check valve to possibly rattle.

The circ is not undersized, it's just trying to get your 20 degree delta wit h the available zones that are open. Is the house and the zones getting to desired setpoint temp?

It's a mixer for primary secondary piping. See Idronics 7 for more details. Paging @hot_rod as Caleffi probably has a replacement.

Mine is still active but since this one has already been decommissioned, and in an attic space, I would leave well enough alone. It will not cause any harm. However, if the homeowner does ask you to remove it, make sure not to tip it over or all the mercury inside will spill out and you will have a serious situation on hand. Let the customer know this as well.

If you haven't already, please watch Dan's video on the subject. Send it to the customer to watch as well. Knowledge is power.

My initial thought is you have air in the pipes that hasn't been purged out. How long has it been doing this?

Try taking out the ifc from the circulator if it's in place. Integral flow check valve. That could be vibrating causing the noise.

" On some zones, as you'll see in the video, the pump runs at around 58 watts while pushing only ~6GPM. Does this mean that the pump is undersized?" Not necessarily undersized. Is 6gpm enough to heat that zone. My experience with this 2218 is it runs full power 58 -65 watts until the delta is satisfied and then it backs off significantly to 7-11 watts until Delta exceeds parameters then it goes back to full power. There is not much for middle ground.

@delcrossv Good catch never seen one of those.

Hello All. I am Installing a new hydronic radiant heating system in an existing home that is currently "gutted" of most drywall and interior finishes. The home is two stories, about 22 years old, and built with modern materials and methods. I have decided to use cast iron radiators for the emitters and each floor will be its own independently controlled zone on its own loop using a reverse return, 2 pipe system. I have already done a thorough heat loss analysis and sized the radiators required for each room. The loop for the first floor will be in the basement with the supply and return to each radiator going up through the floor. The loop for the second story will be run along/though the second story floor joists between the first floor ceiling and second story floor with the supply and return for each second story radiator going up through the second story floor. The piping for the first floor loop (in basement) will probably be copper, and the loop for the second story will have to be pex since I am going to have to drill each floor joist and "fish" it through each one 16" O.C. My question is: in this scenario how does one get the water from the supply loop up and into the radiators? The floor joists in both cases are 2x10s so the supply water will have to be pushed up about 15 inches into the radiator and radiators are 25" tall so approximately 40" of elevation difference. My guess is If I use regular tees for the supply and return to each radiator the water will never exit the supply loop. How is this typically done? Thanks in advance for any responses.

I will add I have sized and installed several radiant concrete floor slabs that work flawlessly but I have never messed with these cast iron radiators yet.