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Faulty mixing valve?

Radiant floor system with Tekmar 360 controlling, a Bosch condensing boiler, and a Buderus mixing station. Buderus has a Danfoss ESBE ARA 663 floating 3-point actuator with a 3-way mixing valve.

Symptom: Radiant floor water temperature getting too hot (140° - 180+°), for too long a period of time (90% of the time).

From a conversation with Danfoss, the problem might be a mismatch between the Tekmar motor speed of 120 seconds and the Danfoss run time of 96 seconds.

The Tekmar motor speed is the time that the actuating motor requires to operate from fully closed to fully open. As I understand it, the mixing valve has a 90° rotation. So if the Tekmar was using 120 seconds, then one of the mixing ports might have gone beyond just open. So in this case, when the Tekmar signaled the mixing valve to close, it might not close completely.

Is my understanding correct?

It might also be a day one misalignment between the 3-way mixing valve and the Danfoss actuator.

My plan is to adjust the Tekmar motor speed to 96 seconds to match the Danfoss actuator.

But I would also like to check whether the mixing valve and actuator are misaligned. Can someone give me a step-by-step how to do this? As a start, from the Danfoss .pdf:

1. When placing actuator in manual operation power should be turned off to the actuator.
2. To manually operate the ARA Series actuator, slightly pull out on large indicator knob.
3. With it pulled out, rotate the knob to the left or right to manually operate the valve.

4. But what do I now do to assure the valve and actuator are aligned?

5. To return the actuator to automatic operation, rotate the knob to the position prior to manual operation and push the knob into the actuator.

Thanks for your inout.



Comments

  • pedmec
    pedmec Member Posts: 655
    there are multiple reasons for overheating.

    1) is the valve actuating. have you used the test feature on the 360 to confirm the valve is opening when it should be opening and closing when it should be closing.

    2) have you set up your reset curve? check the target temperature against what it is sending out after the mixing valve.

    3) is the supply system sensor connected to supply, making good contact with supply, and wrapped with insulation to get supply temperature reading.

    this is just a starting point
    GGross
  • rick in Alaska
    rick in Alaska Member Posts: 1,389
    I would check the sensor.
    Rick
  • jdbs3
    jdbs3 Member Posts: 27
    1) is the valve actuating. have you used the test feature on the 360 to confirm the valve is opening when it should be opening and closing when it should be closing.

    Yes, tests run successfully.
    2) have you set up your reset curve? check the target temperature against what it is sending out after the mixing valve.

    Yes, target temperature matches what is send out after mixing valve, +/- 1-2°.
    3) is the supply system sensor connected to supply, making good contact with supply, and wrapped with insulation to get supply temperature reading.

    Yes.

    Update:

    Ran the system with just radiant floor system. Both Tekmar and mixing station work correctly. They cycling through:

    - Mix (current) > Mix Target = 107, Tekmar Close arrow on, Tekmar flame & boiler on, mix supply/return = ~109°/94°, early in this cycling.
    - Boiler sensor = 130°, Close arrow stays on, Tekmar flame off, boiler off, mix supply/return = 132°/126°, the max values seen for these.
    - Boiler temp (not boiler sensor) gets as high as ~145°. Mix supply/return never gets above 132°/126°, and only briefly at these temps.
    - Continue cycle.

    Now introduce baseboard zone. It does not matter if baseboard was running before turning on radiant zone, or after turning on radiant zone.

    - Tekmar is no longer controlling boiler with a call for or stop of heat. Boiler flame on/off is now controlled by baseboard controller direct connect to boiler.
    - Boiler temp (not sensor) gets as high as 191°. Tekmar close arrow stays on. However, mixing station temp rises peaking as high as supply/return = 164°/154°. Way too hot for radiant floors.

    Based on a conversation with Tekmar tech support, I left Tekmar motor speed = 120 seconds, not 96 seconds to match Danfoss.

    So possibilities for overheating:

    1. Tekmar parameter - I'll talk with Tekmar again, but it does not appear to be this.

    2. Faulty valve - it is looking more and more like this is the problem.

    3. Misalignment between mixing valve and actuator. I would like to see if this is the case before getting HVAC tech in to replace Danfoss ESBE ARA 663 actuator and mixing valve.

    So back to my question ...

    Can someone give me a step-by-step on how to check whether the mixing valve and actuator are misaligned? As a start, from the Danfoss .pdf:

    1. When placing actuator in manual operation power should be turned off to the actuator.
    2. To manually operate the ARA Series actuator, slightly pull out on large indicator knob.
    3. With it pulled out, rotate the knob to the left or right to manually operate the valve.

    4. But what do I now do to assure the valve and actuator are aligned?

    5. To return the actuator to automatic operation, rotate the knob to the position prior to manual operation and push the knob into the actuator.

    And can the mixing valve be replaced separate from the actuator, or are they a matching pair that one needs to buy.

    thanks