No flow on infloor header.

fedupwithcontrols

Just installed a boiler for my 32x56 barn with infloor heat. I have no flow across my infloor header. I thought it was air locked so I bleed each circuit separately until i had no air bubbles in the barrel. Still no flow. I was then looking into the mixing valve. I took it off the piping and found nothing physically wrong with it and it was piped in the correct orientation. I repiped it without the mixing valve and had flow. Anyone else seen this? below is the Caleffi mixing valve I installed. I was running 160 degree system temp, trying to get 100 degree in floor temp.

https://www.supplyhouse.com/Caleffi-521619A-1-Sweat-MixCal-3-way-Thermostatic-Mixing-Valve-w-Temp-Gauge

hot_rod

post a pic of how it is piped

fedupwithcontrols

@hot_rod , supply is on the right. I added an additional check valve on the return, circulator has a check too. I even tried removing the internal checks on the mixing valve think they might be the problem.

HomerJSmith

There has to be a temperature differential across a Thermostatic Mixing Valve for it to properly regulate. My choice would have been a Taco I-series mixing valve with sensor.
No heat energy at the heat emitters is either no flow, or low temperature supply water. You could put a small pump after the mixing valve into the manifold. That would probably give you flow.

GroundUp

You need a circulator on the mixed side of the valve (bottom, in this case) to promote flow through the zone. It'll never work like this.

fedupwithcontrols

@GroundUp makes sense now. I read the instruction but didn't pay attention to the drawing. Live and learn I guess. First time installing one, usually I run one system temp for in floor. This system has other equipment and needed the 2 different temps.

HomerJSmith

When mounting a pump, 10 pipe diameters of straight pipe into the pump and 5 pipe diameters on the outlet of the pump. You will probably need some re-piping.

dko

HomerJSmith said:

When mounting a pump, 10 pipe diameters of straight pipe into the pump and 5 pipe diameters on the outlet of the pump. You will probably need some re-piping.

I've had a question about this, is this needed for low gpm systems such as radiant?
Asking mainly because of the below setups where they break every single one of those recommendations including those for mixing valves. no straight lengths of pipe, elbows, tees, valves. basically all the nonos are combined into the manifold.



Or is this a thing where customer demand outweighs the negatives. Saves space, installation cost, shipping, etc..

hot_rod

Those piping recommendations are all "best practice" suggestions. From pump manufacturers and component manufacturers.
Certainly plenty of close coupled piping components in the real world working just fine. With low flow velocity design, below 4 fps turbulent conditions are not so much of an issue.

Too much flow resistance on the inlet of a circulator is probably the worse of the bunch. With high head circs and high temperature, that is a big invite for cavitation.

hot_rod

fedupwithcontrols said:

@hot_rod , supply is on the right. I added an additional check valve on the return, circulator has a check too. I even tried removing the internal checks on the mixing valve think they might be the problem.

That is not a great check for hydronics. Swing checks need high flow to keep the gate wide open. They can slam shut due to the long travel distance, and they need a pressure differential to seal tightly. That is probably a 12- 15 Cv valve with maybe a 4 gpm flow going through it? Good chance the gate inside will never get pushed up into the Y out of the flow 100%. Conical seat spring checks only in hydronics is my recommendation.

You don't need it, and if it does cause noise issues, remove the cap and pull the disc out of it. Same with the strainers and checks that come with some model of thermostatic valves, scrap them also in hydronic applications.

Yes the pump is a must on the mix port of a 3 way valve.