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Tekmar 279, BOILER DESIGN PERCENT not impacting overall heat delivery

rhodebump Member Posts: 152
edited January 2023 in Thermostats and Controls
Tekmar 279 installed.

Condensate sensor installed
Outdoor temp sensor installed
Indoor temp sensor installed, but disabled via dip switch.

Building is over-heated (by 10 degrees)
SET the BOILER DESIGN PERCENT TO 80%, and let it run overnight, no temp drop.
SET the BOILER DESIGN PERCENT TO 50%, temp is dropping now.

Are there any guidelines in setting this? I would have thought that setting at 80% would have dropped it by a few degrees at least.


  • KC_Jones
    KC_Jones Member Posts: 5,742
    You might have to go lower, depends how oversized the boiler and system are for the building.

    For example, if the system is perfectly matched to the heat loss on the coldest day, and the boiler is perfectly sized to that, then the setting in theory is 100%.

    If the system is oversized for the heatloss and the boiler is perfectly matched to the system, you would drop the percentage accordingly.

    Now if both things are oversized then you would have to drop it even more to allow for both things being oversized.

    If you knew the building heatloss and the system EDR, you could run some numbers to get a baseline of about where you should be, but without that, just keep adjusting until it's hitting the temperature you want. That is basically what the instructions say, they just don't address how grossly oversized the steam systems and the boilers can be.
    2014 Weil Mclain EG-40
    EcoSteam ES-20 Advanced Boiler Control
    Boiler pictures updated 2/21/15
    EBEBRATT-Ed Member Posts: 15,624
    Just have to fiddle with it to get it right. Where is the condensate sensor located? That is used for the steam established sensor. It is better to have it at the far end of the system rather than in the boiler room. I find that control pretty easy to work with.
  • JohnNY
    JohnNY Member Posts: 3,231
    The *Steam Established* setting provides the most reactive feedback to the control in my experience. That and Cycle Length. There are many options on that control to get your curve right, unfortunately it generally takes several tries to bring it to where you want it.
    Contact John "JohnNY" Cataneo, NYC Master Plumber, Lic 1784
    Consulting & Troubleshooting
    Heating in NYC or NJ.
  • rhodebump
    rhodebump Member Posts: 152
    The condensate sensor is located in the boiler room on the condensate return (right below from where we have the vents)
    It's set for 1 CPH

  • rhodebump
    rhodebump Member Posts: 152
    I had set the BOILER DESIGN PERCENT to 50% and let it go for 4 hours. No decrease in heat produced. Still running high 80's

    I have 8 sensors (using ecowitt) and gives me a good view of temps for each sensor with graphs https://www.ecowitt.net/home/share?authorize=VTGM7F
  • rhodebump
    rhodebump Member Posts: 152
    I read (a few times) the tekmar install manual and I think I have a potential solution.

    I installed my condensate sensor in the boiler room and went with the default value of "180" degrees (default). Since this sensor is not installed on the last radiator, I need to use the 2-way radio (but will use mobile phones) method described and get a more accurate temperature. I suspect that I will be lowering this setting and this will shorten my heating cycles.

    Any thoughts on this idea?