Is my Modcon plumbed correctly?

wattz24

Hello heating pros. I have a question about my new to me home. It has a buderus GB142-45 heating a 4200 sq ft home. With all in floor pex radient. The reason why I am wondering if it was plumbed correctly is that it’s using a tekmar 361 to control the boiler and mixing pump. The 361 wants to run the boiler at 190+ degrees and I know to get max efficiency I need to be closer to 120ish correct?

It seems from my research the boiler was installed in 2005/2006 prior to the am10 outdoor reset. The 361 does have a outdoor reset and will pull back the mixing pump when it sees to high heat in the pipes. That ofcourse causes the buderous to over temp and shut down since I had manually set the temp for 120 degrees. Since that seems to be the only wat to keep it in its efficiently range.
Any ideas would be very helpful.
Thank you.

SuperJ

Your venting looks discolored.
190f for indoor is insane even if your mixing it down.
The injection loop is probably inappropiate for a modcon, it basically assumes your boiler SWT is higher than what your load needs.

https://www.bosch-climate.us/files/6720820104_GB142_Installation_Instructions_en_10.2017_US.pdf

Need to get a outdoor reset working. You may only need 120f on the coldest days. You could probably be under 100f a lot of the time. But it's important that the boiler setpoint gets reset down, not just the injection setpoint.

It looks like you need a AM10 (outdoor reset control), or RC35 thermostat to get outdoor reset functionality working in the boiler.
https://www.bosch-climate.us/files/GB142_applications_manual_US.pdf

In the absence of a ODR, keep turning down the boiler setpoint dial until you start to experience comfort issues, and then bump it up slightly. Don't worry about if you have zone continuously calling unless it's actually cold in the space, ideally you want your infloor zone valves open for hours at a time.

Your boiler probably has a 3 speed pump, you want to select the speed based on temperature delta at high fire typically somewhere around a 25F delta at high fire is safe. If the delta is lower than it means you have hot water going around in a circle, and warming up your return killing efficiency.

For efficiency you really want to reduce the boiler entering water temp as low as possible. With infloor 120f or lower return temps should always happen. Unless it's high temp staple up. Is the infloor tubing in a slab or just inbetween you floor joists?

I wonder if the injection loop control was added to makeup for the boiler's lack of built in control? Or did the injection loop predate the modcon? Was there originally a cast iron boiler that needed protection? I see the old vent hole plugged in the wall. You maybe be able to just connect the primary loop to the injection loop tees on your secondary, and ditch the injection pump and controller.
I don't really think that controller is the best match for a low mass modcon since it basically just turns the boiler on and off.

The tekmar controller is fairly well documented, you should go thru the settings and make sure they match your setup (probably high mass radiant). Also, make sure all the sensors are installed and functioning properly (if they're strap on they need good contact with thermally conductive paste and then a wrap of insulation.)

http://www.tekmarcontrols.com/images/_literature/361_d_06.pdf?lbisphpreq=1

Zman

The venting color is alarming. The heat exchanger in that type of boiler has tenancy to plug up. I suspect you are running very hot flue temps. It is also possible the vent is run in cellular core piping rather than solid core.

As for the Mod/CON, you are correct. At 190 degree you are only MODulating, no CONdensing going on there, so no high efficiency.

I would cut out the injection mixing and set the boiler up with either the OEM outdoor reset module or a third party controller

hot_rod

Or it it CPVC, that tends to be tan colored?

Adolfo2

Zman said:

The venting color is alarming. The heat exchanger in that type of boiler has tenancy to plug up. I suspect you are running very hot flue temps. It is also possible the vent is run in cellular core piping rather than solid core.

I noted the yellowish discoloration in the exhaust venting as well BUT the cold inlet air pipe is the same color which makes no sense to me.

NY_Rob

Could the PVC discoloration be due to the florescent lighting?

I think I recall reading something on that once....

Gordy

In would be interesting to know if all the in floor radiant needs same supply temps.

I see no reason to run a mixing station as @Zman points out. Let alone 190 plus water temps.

What is the radiant panels design criteria? Staple up? Suspended tube? Plated? Sandwich? Concrete? Gypcrete?

wattz24

I belive the piping is CPVC hence the coloring. You can see the intake pipe is the same color. As for flooring the majority of the house is in slab on grade. But a small portion is staple up I belive? I’m not sure since the basement is finished and the part I can see is covered in open cell foam insulation so I can’t say if that area is under or over the joists.

So would you think I just take out the injection pump? And just make it one primary loop? Or would it be worth it to get something like the buderus low loss header? I also have a DHW loop but that runs separate from this primary heating loop.

I think the injection loop was put in because the installer had no idea what to do with this type of “new fangled” condensing boiler. It was installed right when these just came out in the states. Circa 2005/2006.

Zman

You can just pipe it primary/secondary using closely spaced tees if you want to do it simply.
I would definitely clean the heat exchanger and have a combustion analysis done. That particular "new fangled boiler" needs to be cleaned regularly or it will cease to function.

Zman

The buderous header is nothing special. In my mind it is a poor design. None of the components have the recommended separation.