radiant heat - low circulation problem


Hi - I'm building a new house in the Boston area and installed a Warmboard radiant system with Viessmann wall hung condensing boiler. I'm having problems getting this system working correctly. It appears as if I'm not getting enough circulation. The Grundfos UP26-64 pump seems to be powering up and running (I even took the cover off and confirmed it was spinning and there are no noticible dings or scratches in the plastic impellers). I was able to fill the system fine, but I appears as if I'm only getting around 2-3 GPM total for the entire system at the manifold, even when I turn off all manifolds except for a small one with only 4 loops. The Viessman is outputting 25 psi.
When I run the boiler at a 90-95 degrees, it doesn't even come close to heating up any of the tubing. After cranking it up to 150 degrees, the house is now warm, but I'm pumping (and wasting) a lot of heat.
Seems like a circulation issue? Anyone have any ideas? Bad pump?
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I don't know a lot about boilers other than what I have read here and what I pick up from the guys who fix mine now and then.
I can tell you that mine is typically at 180 degrees and 20 pounds of pressure by the gauge on the side of the boiler. I have no idea how much the pump puts out. It just works.
I'll be interested to read replies from people who know about these things.
I'm not sure why you say you are wasting heat by having it set higher. The hotter water returned to the boiler just goes around again. I don't see where the waste would be, but I could very well be missing something.
Tom
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After 2 hours of playing around and swapping pumps, I figured this out last night. My plumber had put a mixing valve in between the low loss header and the radiant controls. I guess this isn't usually a problem, but for some strange reason my mixing valve isn't working right... when I shut it off, I now get full flow at all my 6 manifolds. With it on, I get almost no flow. Weirdest thing - plumber and my radiant designers can't figure it out, but the valve is coming out ASAP.
Tom - not sure about your system, my radiant designers did all the heat loss calculations for my house and tell me I'm supossed to be able to run this system at 90-95 degrees. Obviously, if I'm not getting enough flow to the manifolds, the water isn't moving fast enough thru the system, and the system doesn't heat up as quickly (if at all)... especially where I'm doing a cold start when it's 20 degrees outside. It was losing most/all of it heat just running between the boiler and the manifolds. Thus, my boiler was working overtime heating up water to 90 degrees plus and we weren't getting this heat into my system - so it was "wasted". To compensate, I had to crank the boiler up to 140-150 degrees, just so we could get some heat into the system. They also tell me that under stable conditions, the drop from your supply temp and return temp should be 15-20 degrees.... I was getting something like 70 degrees drop and still not getting the house warm.
Now with proper flow, I should be able to run it at 95 degrees and still heat my whole house (saving a lot of energy vs heating to 140). Plus these boilers are [supposedly] designed to run these systems - it has different settings depending on what kind of heating system you're using - radiant, baseboard, etc.
I just cranked the boiler back down, but they tell me I should be able to run the boiler at around 100 degrees, my supply lines should be around 90 degrees and the return lines should be around 70-75 degrees. We'll see. This is my first time with radiant, I've spent a lot of money on it, i'm just hoping it works...
Anyone else have problems with these mixing valves?
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elai wrote:

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elai wrote:

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elai wrote:

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