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Heating system setup question (Boiler Demand on Tekmar 256)

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vciecierski
vciecierski Member Posts: 13
edited December 2022 in THE MAIN WALL
Hello, we just moved to a new place with the following setup: Buderus G115/5 boiler (with Tekmar 256 OTR and Honeywell Aquastat L8148A 1124). SuperStor 80G indirect water heater. 2 Air handlers. Grundfos circulator. There are three Taco valve zones (1 for the SuperStor, 1 for AH in attic and 1 for AH in Basement). 3 Nest thermostats. I am no expert by any means but I noticed a few things that don’t make sense to me:

1. Tekmar’s temperature sensor is connected to the RETURN line, not SUPPLY like I would expect. Is this normal?

2. Aquastat has only upper limit control and is set to 180. With this temperature on the Aquastat, the Tekmar and the circulator do not behave the way I would expect. Basically when there is a call for heat from the thermostats, the taco valves open sending a signal to the Tekmar, Tekmar then displays “Boiler Demand” BUT it does not trigger the circulator and/or boiler. I expected the boiler demand on the Tekmar to trigger the circulator and the boiler (if temperature is not hot enough). Only the "burner icon" on the Tekmar triggers the circulator and boiler to turn on simultaneously. When the Aquastat detects the upper limit temperature, it turns off the boiler and keeps the circulator running. Is this normal (the boiler demand not triggering anything)?

Any info on this set up would be greatly appreciated. Thank you!

Pictures for reference:



Comments

  • hot_rod
    hot_rod Member Posts: 22,472
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    Tekmar manuals do a good job of explaining the operation and showing how it should be wired and configured. Did you trace out all the wiring to the tekmar.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    vciecierski
  • vciecierski
    vciecierski Member Posts: 13
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    Thank you for linking the manual. I still don't see how the tekmar could "send a signal" to the circulator independently of the boiler (depending on the water temperature in the boiler). Looks like tekmar has only one "output" to the boiler (terminals 5 and 6) and nothing to the circulator.
    How about Tekmar’s temperature sensor on the return side? Shouldn't be this way, right?
  • hot_rod
    hot_rod Member Posts: 22,472
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    The sensor should be a few inches downstream of the circulator. It needs to know the boiler supply temperature to the system
    Arrow on the zone valve indicates flow, same on the circulator. Assuming it is piped correctly? Pumping out of boiler supply, zone valves on return side?

    The control operates the boiler. The main circulator is probably wired into the boiler control. Wires from the zone valve into the box on top of the boiler, close a relay to start the pump. Follow the wires. It is nice to draw a wiring diagram as you trace wires.
    Ideally the installer would leave behind a wiring diagram and sequence of operation, especially when multiple after market components are used, zone valves, tekmar control, additional transformer were all added onto the basic boiler, they need to work together.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    vciecierski
  • vciecierski
    vciecierski Member Posts: 13
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    Thank you for your reply.
    Maybe I am not phrasing this correctly, but my main issue is this: in a correctly set up system, should the "boiler demand" indicator on the tekmar somehow turn on the circulator (assuming the water temperature is hot enough) independently of the boiler? Does it have that capability? In other words, what is the difference between the "boiler demand" indicator and the "flame" indicator on the tekmar? Thank you again!
  • hot_rod
    hot_rod Member Posts: 22,472
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    The 256 is really just a switch. It will turn on whatever you wire across that 5-6 terminals.

    As the wiring diagram shows, in this example, an additional relay was added to the 256 to turn on the circ.
    In your case it sound like the 5-6 wires to the boiler and the boiler relay turns on the circulator. At least from what I see in the pic.

    You need to trace wires, or use a volt meter to see where the various components, like the circulator get powered from, where 5-6 goes. I suspect into the relay box on top of the boiler, in there the 120V feeds to the circ. See the terminals in the box on the boiler labeled circ, bottom left? That looks to be powering the circulator.

    The boiler demand light indicates there is a call for heat to the control, The left side 1234 are sensor inputs.

    5-6 is the actual switch. 8-9 is where you power the control with 24V

    If you want the circulator to run whenever the 256 has a call, then you need to wire it like this diagram, through a separate 24- 120V relay. The zone valve end switches call on the circulator through the tekmar #7 in this wiring.

    If you want the circ to run only when the boiler is running, then the circ wires to the boiler control box, as it looks like it does now.

    So it comes down to whoever installed and wired it, what they had in mind. Since the sensor appears to be in the wrong location, they may not had a grasp of what the options were?

    Regardless, what do YOU want it to do?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • vciecierski
    vciecierski Member Posts: 13
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    Everything you said is correct regarding the current operation/setup. I even bought a switching relay for the circulator BUT I got stuck with how the indirect water heater would operate with the new setup. I did not end up connecting the relay (yet).
    Please correct me if I am wrong, but the tekmar should not be in any way connected to the DHW circuit (I am assuming this because if on a warm day the tekmar calculates a low target temperature, it would not be enough to heat up the indirect water heater). I am guessing, the indirect water heater should be directly wired to the aquastat bypassing tekmar - but if this is true, how can I have the new circulator relay wired to DHW and tekmar? In other words, my assumption is that tekmar is designed to work as a home heating tool/control, not a DHW control.
    Thank you so much for your help on this!
  • hot_rod
    hot_rod Member Posts: 22,472
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    Correct. There are versions of tekmar that have DHW function, yours doesn't
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • vciecierski
    vciecierski Member Posts: 13
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    So..... basically... this version of tekmar is absolutely useless in this application? Oh, and btw, I tried moving the temp sensor to the supply side of the boiler but that caused the air handler to blow in cold air since the circulator would not run in that configuration. Do you recommend any hardware to improve the "efficiency" of this system? Any modern controls/aquastats/OTR?
  • hot_rod
    hot_rod Member Posts: 22,472
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    You have a basic boiler reset control. You could get a more robust version of a tekmar, or a good control guy could build a control with off the shelf parts.

    It sounds like you would like to reset the boiler for the AH loads, generate DHW with high temperature, and a radiant low temperature loop also?
    You kinds need to define the system and pipe it to match up with the type of control logic you want to control the whole system.
    Do you know the lowest temperature you can operate the AH on a cold design day? You could simply run the system at that temperature, say 170F. Then all the high temperature is covered. Mix down with a 3 way if you go with garage radiant. That is as simple as you could do it.

    The ODR control would pick up some efficiency by modulating the boiler SWT, maybe 150- 180 as an example. But as you see it gets more complicated to cover the DHW load. On a DHW call ideally you trigger the boiler to ramp up to 180F or so. Regardless of what the ODR is telling it to run. A double throw relay could drop all heating loads when DHW calls and bypass the tekmar to run the boiler up hotter.

    Is this something you want to tackle on your own? Without control knowledge, it could be a $$ and frustrating endeavor. At the very least hire someone to draw up a proper wiring schematic to match the system you have. Or want.

    Here is an example of a proper design and documentation, for a fairly complex heat, cool, DHW system.

    Maybe you could hire @EdTheHeaterMan, Duke of Oil to come up with a design :)

    Piping schematic, description of operation, and wiring diagram to match.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    EdTheHeaterMan
  • vciecierski
    vciecierski Member Posts: 13
    edited December 2022
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    There is no radiant anywhere in this house. Just two air handlers (one in the basement and one in the attic) and one indirect water heater. 3 taco zone valves.
    I really don't understand how and why the previous owners set it up this way, pointless/useless application of the OTR.
    Anyway, I just spend some time researching potential upgrades, looks like tekmar 260 would solve my issue.
    And yes, I am starting to think a pro is needed here :)
  • hot_rod
    hot_rod Member Posts: 22,472
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    You have one of the better systems in which to apply ODR. The high temperature systems see the most benefit.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,166
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    When did I get a demotion to Duke? @hot_rod

    How would like it if I posted you as the Master of the Hot Rod bumper car circuit?
    Respectfully submitted by
    @EdTheHeaterMan King of Kombustion.


    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • hot_rod
    hot_rod Member Posts: 22,472
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    I had that old 60's hit in my head duke, duke, duke Duke of Oil (Gene Chandler)
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    EdTheHeaterMan
  • hot_rod
    hot_rod Member Posts: 22,472
    Options

    When did I get a demotion to Duke? @hot_rod

    How would like it if I posted you as the Master of the Hot Rod bumper car circuit?
    Respectfully submitted by
    @EdTheHeaterMan King of Kombustion.


    I'd like to find an old bumper car actually. To build one of these!
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    EdTheHeaterMan
  • vciecierski
    vciecierski Member Posts: 13
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    I just wanted to say thank you to the forum members and everyone who helped me with this project. This is truly an amazing community.

    I ended up installing the Tekmar 260 all by myself (thanks to this forum) and could not be any prouder of myself. Thank you again!

    Finished result: