Radiant Heat Flow Issues

VTommy12 · April 9

Hello! I've been battling an issue with my radiant heat system since it was installed 7 years ago.

It's an IBC DC33-160 condensing boiler servicing radiant heat (1st floor) and base board heat (2nd Floor), propane.

We simply can't get flow through the radiant heat manifold. There is a circulator pump within the boiler and also a larger external circulator pump. If I shut the boiler off for a while and then turn the system back on I will usually get flow…. after 5-10 minutes, the flow immediately stops. Once the flow stops, if I unplug the internal pump we'll get our flow back after 5 minutes or so. It appears that these two pumps are working against each other.

Note: I was able to completely turn off the boiler and run the external pump as a test and I had constant flow.

I'm hoping someone has dealt with this in the past! No plumbers seem to be able to crack this one.

Thanks!

DCContrarian · April 9

It's hard to follow everything from just the picture but it looks like the tempering valve in plumbed wrong. I don't see how there's any flow when the supply temperature is above the setpoint on the valve, the valve just shuts off the hot and there's nothing to make the cold flow. The pump has to be inside the loop where it provides flow regardless of the setting of the valve.

VTommy12 · April 9

Ah, I see what you mean. So must be in that 5-10 minutes after firing up the boiler, the water gets hot enough to where the tempering valve closes off all of the hot water to the manifold, even when set at the hottest temperature?

Kaos · April 9

The low temp rading and mix is definatley plumbed wrong. Can you do a sketch of the rest of the plumbing (start from the boiler supply and trace all pipes, pumps, valves till you get back to the boiler return). There might be other issues with the setup.

hot_rod · April 9

The piping should look like this at the 3 way valve. There needs to be a pump on thje mix port of that 3 way valve, mit pull hot and cold to mix.

The cold port of the three way valve gets the return manifold and also returns to the boiler

Generally 6- 8 loops on a 3 Cv valve like that. That is what the X refers to in this drawing.

It depends on how many gpm each loop needs. A total of 5- 6 gpm is comfortable for that mix valve.

But it definitely needs a circulator at the valve.

VTommy12 · April 9

Thank you so much for these comments. I've attached a slightly better picture of the whole system. If I added a 3rd pump post mixing valve, do you think that would be too much GPM for the system?

Also, with the limited space available the new pump may be close to an elbow on both the supply and return. Is that ok?

Mad Dog_2 · April 9

Where is this job located? Mad Dog

psb75 · April 9

You HAVE to have the secondary (Grundfos) circulator RE-PLUMBED so that it is PULLING from the "mixed' port of the tempering valve. I don't know why hot_rod's schematic is "x"-ed out, but…..like that! It's hard to believe that the radiant zone ever worked right.

VTommy12 · April 9

VT

psb75 · April 9

VT? More specific: north, central, south?

GroundUp · April 9

It's not as simple as just adding another circulator. The supply needs to be repiped in a fashion that doesn't allow the existing external circ to be pushing at the mixing valve at all, which is going to get very messy with the tight space and press fittings- personally I'd cut most of it out and start over. My $.02 would be not to call any of the supposed "plumbers" that couldn't figure this out, it's very basic knowledge for anybody who works with hydronics.

hot_rod · April 9

Here are a couple piping options. The top uses closely spaced tees to tie boiler to l;arge header.

The lower uses a hydraulic separator, a nice option as you get air, dirt, magnetic and hydraulic separation in one device.

If your loops ar .5- .6 gpm each, which is common for 1/2' loops, that valve will be adequate.

Is there any design data available for the system?

smittytheplumber · April 17

seeing as you need to repipe you should do yourself a favor and make it outside temperature responsive with a motorized mixing valve or an injection pump. This will eliminate the flywheel effect and give you the comfort level you deserve with radiant.

Radiant Heat Flow Issues

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