Tekmar 360 settings "Mix Target" versus :"Boiler Min"

Jay_H

HI folks, I moved into a house with a low mass radiant system with a Viessman VT100 boiler, a tekmar 360 and a tekmar mixing valve (Forget the model, not too important now).

I'm learning the system and have studied the manual to figure out the numerous settings. I know the theory behind keeping the boiler temp above 140degF to prevent flue gas condensation. But I think there seems to be a contradiction in the settings which may be a lack of understanding on my part or perhaps a manual that isn't clear on the thing.

I understand the boiler min to be the minimum temperature for the 360 to open the mixing valve. So if say the boiler min was set to 180degF, the 360 will not command the mixing valve to open until the boiler supply is registering (close to) 180degF. I tested this by setting the boiler min to like 120 and watched once mixing demand was triggered the boiler temp rise and the mixing valve opened.

However, it seems to me that this contradicts the definition of mix target. For argument sake here, say the 360 is set to setpoint control, which is a fixed mixing target. without the need of an outside sensor. What happens if the mix target is fixed at 140deg? From the manual, this sounds like the mixing valve will never be opened and the heat will never work. because if the 360 is trying to send 140deg through the distribution, the boiler min will prevent the mixing valve from opening and this to me sounds like a contradiction or a stalemate. What am I missing? Will the 360 simply keep firing the boiler until the boil temp reaches 180deg overriding the mix target or will this be an endless tugowar? To me, as a software engineer by trade, this is a software design issue and essentially the boiler min overrides the mix target. I would think some kind of warning or say indication would be a nice thing.

Can somebody explain the precise steps of the operation given this scenario?

Jay

Zman

The controller is modulating the mixing valve. It is not an on/off operation.
In your scenario where the boiler min is set at 140 and the mix target set at 140, the mixing valve will begin opening when it sees a boiler return temp above 140. It may not put out the full 140 to the mixed side at first, especially if it is trying to heat a high mass slab. In a properly designed system, eventually the laws of thermodynamics will take over and the boiler will be able to keep up with the load.

Jay_H

I do witness the slow opening speed but I woke up one morning to the downstairs being like 59degs when the tstat was set to like 66. This is after I witnessed normal operations that whole day. (We had to have the old Oventrop mixing valve replaced) so this is a new tekmar unit. I go downstairs and notice the mixing valve completely shut and the mix temp at 61 degs (room temp). Since I had to go to work, I simply turned the mixing valve to manual and opened it, heat then flowed and everything is good but this had me wonder about the scenario above.

Something was wrong if the temp was only 59 and the mixing valve was fully closed. I then after studying the manual checked the boiler min setting and it was set to 180degs.

The next day, as a test, I set the boiler min to 120deg and everything was normal, the heat worked, I watched the valve open when the boil temp was nearing 120degs.. So that led me to conjecture of this possible stalemate condition but maybe that is not the case or 180 is way too hot.

I've been slowly moving boiling min up from 120degs as recommended but keeping the mix target a set point to avoid too many variables into this... It sounds to me from your response that the 360 should wait til the boiler reach the boiler min and then open the valve to heat the supply and then modulate it when it hits the mix target. For some reason on that morning when the downstairs was 59, I don't believe it was doing that OR the system could not handle the required heat (OR) my settings need to be further tweaked (quite the possibility)..

Jay

Zman

The Tekmar should be reading the return temp for the boiler. If you had the Tekmar minimum set to 180 on the return and the boiler aquastat set to 180 on the supply, the Tekmar would never see it's minimum boiler temp and would not turn on.
It sounds like you just had some incorrect settings.

Jay_H

OK, I believe the aquastat on the boiler is set to about 160 at least there is a temp/pressure gauge on the boiler itself and the needle is sitting at 157-160degs..

If I reduce the boil min to 140, the boiler should have no problems attaining that temp if I understand this correctly. I'm gonna go change my boiler min setting up to 140 from 120 which is what it's currently set at and run that for a few days. After that, I will change it to the intended Outdoor Design but I don't want to introduce too many variables at once...

Thank you for the help! Sometimes, I wish I just had my wood stove.... :-)

Jay

Jay_H

Update, well last night I changed the boiler min to 140degF from 120degF and no go. This morning the mixing valve was fully closed and there was no heat throughout the house, downstairs was 54deg and upstairs was just about 60deg?

What does this mean? does this mean that the boiler cannot supply 140degF water and then the 360 doesn't open the valve as I originally conjectured?

Could this be the aquastat temperature on the boiler itself? If so, any clues on how to set that to perhaps raise it? I turned the boil min temp back down to 120 and I can see the valve now commanded open and heat is flowing again. I can try to inch the boil min up to the point where I can see it fail but this sounds like perhaps it's a boiler issue. I still think there is a design flaw in the 360. Like perhaps it should have a timeout value if the supply never reaches 140degs within X minutes to indicate something wrong with the supply...

Jay

STEVEusaPA

How about a picture of your boiler's near piping, showing the controls.
After that we can open up the manual and go thru each setting step by step.
Is this a Vitodens 100W? condensing gas boiler?
I have a feeling the settings on the boiler control are conflicting with the Tekmar settings.
BTW, was it working correctly before you started adjusting?
Is the original installer's number on the boiler?

Jay_H

Yes, a Vitodens 100W (oil) boiler...

I, unfortunately, do not have a lot of history here, the heat was not working 100% correctly when we moved in so I have no baseline to compare. I vaguely remember the person who removed the old Oventrop told me he lowered the temp of the Vitodens 100W so I suspect this is most likely the culprit.It makes total sense to me if this is the case, He, unfortunately, never returns my phone call so I had a different contract come in and replace the mixing valve with the tekmar one. I suspect that this is the case so hopefully all I need to know is how to turn up the boiler once more.... I'll take some pictures tonight. I have the manual and I can venture into the unit once I study it some...

Jay

STEVEusaPA

W is condensing gas, just 100 is oil. Please get exact model #.

Also, look at my comments here about Tekmar, injection & boiler minimum temp and see if some of that may be happening to you:
https://forum.heatinghelp.com/discussion/comment/1546974#Comment_1546974

Jay_H

Sorry, it seems Viessman has a fascination with V, vitodens, viterond... The fact that I'm doing this not at home means it's not in front of me.

I'd have to find out the exact submodel of it (VRx). It has a mfgr date of 2005 and has a Outside Air Kit