Taco iSeries mixing valves hunting season

AKDISTILLER

I had a couple iSeries 3-way mixing valves installed recently and they just constantly adjust back and forth hunting for their target temp and not coming even close. I can monitor my temps on my Taco 00e and can tell the valves go from fully open supply to fully open return not ever slowing down when they are at their target temp. Has anyone else experienced this with these mixing valves or know why they might be doing this?

EBEBRATT-Ed

Need some pictures of how it's piped and what do you have for sensors? Boiler supply, boiler return, outside air?

Cold be a sensor issue could be a piping issue, could be the valve installed is too large for the flow if they line sized the valve. Dip switch settings??

AKDISTILLER

I dont think much thought was given to sizing the valves. The valves are 1", one is on 1" pipe on the small building circuit (1400 sq' radiant) and the other is on 1 1/4" reduced down for the valve on the large building circuit (3300 sq' radiant) The dip switches are set at 1-on, 2-off, 3-on, 4-on. The outside air sensor are installed and supply and return sensors have been triple checked that they are correctly installed. I have swapped out the sensors without any change in performance but not tested them.

EBEBRATT-Ed

Hard to tell. I would download the spec sheet for the valves you have. You can find them at Supply House.com.

Someone is going to have to take the spec sheet and figure out what's going on.

Check to see if the valves are piped in the correct orientation

Check dip switch settings

Remove sensor wiring and ohm out sensors

Confirm sensors are located where they should be and tightly attached to the pipe

Confirm power to valves

As far as the valve sizes they look reasonably close. The reason I asked was a control valve that is too large can give unstable control.

I don't know what boiler water temp your running at but just for the fun of it drop the boiler water temp 20 degrees and see if it changes the valve operation.

Don't run the boiler below 130 degrees return water for an extended period of time

GroundUp

I have never seen an iSeries that actually worked correctly. If they're not hunting, they're way off.

Zman

Valves will hunt like that if you don't size them carefully to the flow rate. You generally want the CV value to be close to the flow rate. Sometimes that means going with a valve that has a reduced pipe size.
Do you have the circulators running in delta T mode?
I wonder if the 2 controllers are competing with each other. If you put the circ in a fairly high fixed speed mode does the problem get better?

hot_rod

You want to measure temperature a few feet downstream of the mix valve. It takes some distance for the two temperatures to blend. It is critical to size a ball valve, really any control valve by the Cv.
It is not uncommon for a Caleffi Legiomix ball type mix valve to be a couple pipe sizes smaller than the piping.

Also on DHW systems the piping in the building is over-sized, sometimes grossly oversized. The next Coffee with Caleffi talks about how to correctly size DHW piping with the latest data and calculators.