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Tekmar 353 not telling my variable speed pump to run fast enough

tctran_jm3
tctran_jm3 Member Posts: 4
edited November 2022 in Radiant Heating
Thanks in advance for any helpful answers.

I have a radiant heat system that has given me problems for the last year. The home is 20 years old and I don't remember having issues in the past.

My thermostat is set to 70 and the room temp struggles to stay above 64 degrees. Outdoor temp is 40. I have a tekmar 353 mixing control that varies the speed of a grundfos pump. The pump is a year old. I set the Heating Curve setting to 'Setpoint A' and the Max Supply / Min Return to 160. Last year this setting worked like a charm. When the system 'works', the "Max Supply/Min Return" light would stay off and the % out light would stay almost solid or blink very fast. I think this means the pump is pulling more hot water from the supply line and thus getting more hot water into the radiant floor tubes. Today, with the heat not really working and the radiant pumps staying cold, the 'Max Supply / Min Return' light is a solid red, and the % out light is blinking very slowly (I believe this means very little hot water is being pulled from the supply line). Even when my supply line goes cold from the returns, the 'Max Supply / Min Return' line stays red. Does it sound like my tekmar 353 mixing control is not functioning properly? Is there anyway to trick the mixing control so that it doesn't think the 'Max Supply / Min Return' has reach it's limit? The setup includes a tekmar 251 one stage boiler and DHW control.
This is what I pulled from the manual.







Thanks.
Tom.

Comments

  • Zman
    Zman Member Posts: 7,433
    Are all of the sensors securely attached to the pipes? Do you have a way to measure the actual supply and return to the zones? How hot do the feel?
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
    tctran_jm3
  • hot_rod
    hot_rod Member Posts: 18,195
    This is running an injection mixing circulator? You could just wire that injection circ to a plug, run it full speed to see what SWT you get
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    tctran_jm3
  • tctran_jm3
    tctran_jm3 Member Posts: 4
    Zman said:

    Are all of the sensors securely attached to the pipes? Do you have a way to measure the actual supply and return to the zones? How hot do the feel?

    I have concerns if the sensors are attached correctly. The supply side sensor is attached before the variable speed pump. The rerun sensor is in an odd spot, it’s above a second variable speed pump. The sensors and tekmar mixing control are 20 years old.


  • tctran_jm3
    tctran_jm3 Member Posts: 4
    hot_rod said:

    This is running an injection mixing circulator? You could just wire that injection circ to a plug, run it full speed to see what SWT you get

    Yes, I believe it’s and injection circ. Fyi, I’m the home owner and not very experienced with this. Have had 4 plumbers come in and no one seems to know about these tekmars.
    Thank you
  • tctran_jm3
    tctran_jm3 Member Posts: 4
    Zman said:

    Are all of the sensors securely attached to the pipes? Do you have a way to measure the actual supply and return to the zones? How hot do the feel?

    I don't have a way to measure temp on supply or return. Using my hand, the supply can get quite hot. It's hot for quite a long time. At time during the day, it's quite cold. The return is always cold, because it doesn't seem like much hot water is being pumped up. Thanks.
  • Paul Pollets
    Paul Pollets Member Posts: 3,568
    The sensors are usually insulated with neoprene to eliminate drafts around the sensor and get a more correct reading. You need to find an experienced Tekmar tech who can diagnose and repair.