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Troubles getting Radiant Heat up to temp

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Looking for some tech help with a 20 year old system. I have two hydronic manifolds that try heat my home. The first is a closed loop manifold that includes a boiler pump and four zones with circulator pumps. One DHW zone, two hydro air zones and one zone that acts an an injection pump for a second radiant heat manifold in a second basement 60 feet away. I have 8 Taco circulator pumps (in total) on both manifolds (including the boiler pump) and all are 007-F5s. I have replaced several corroded 007s over the years and now in the process of replacing my entire radiant manifold pumps. The entire radiant manifold (3 zones) has been completely flushed and bleed but I can not seem to get supply water above 100 degrees to my radiant floor tubing. The supply pump and the injection pump are only two years old and the mixing is done by a Taco PC 705-2 variable speed mixing control. The heat coming from the injection pump is 160 degrees and that showed when I was bleeding the radiant zones with the boiler make-up valve. When the system is turned on the supply pipe manifold is scalding hot but when it gets to the tee where it splits to the return zones and supply zones it instantly drops to touch and zones display water temps of 100 degrees. If I close all supply and return zones on the radiant manifold I instantly get scalding hot water going back to the return side of the injection pump. I am sure the radiant zones are not air bound. All three zone circulators are brand new. What I am left with questioning.... is the PC 705 malfunctioning, is the injection pump undersized, is the boiler pump undersized. Any thoughts or tips would be greatly appreciated...Thanks!

Comments

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,176
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    @hot_rod has the answers to this type question. There is an adjustment needed or a mixing sensor is not operating the mixing pumps properly

    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: 22,505
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    it doesn’t take much pump to inject 160 f down to 100 or so. A 007  should be plenty

    if you suspect the control is bad, wire the injection pump directly to the 120v in the control. But it sounds more like the zone pumps not flowing the injection mixed flow?

    You mentioned corrosion, any strainers in the system? We have seen a few plugged air seps here recently. Any other device in the piping that could be partially turned off?


    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • CHRISHALL
    CHRISHALL Member Posts: 9
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    Thank you both for a quick response... I was skeptical anyone would respond. There are NO strainers in my system and we flushed the entire system from the boiler through all radiant tubing. Some of my circ pumps are pushing 20 years old and are beyond their time of replacement. The water was muddy colored when we flushed the radiant tubing but not thick. We flushed this same system two years ago and it was thick as soup. After we flushed we also bled the system using the boiler makeup valve we exhausted each zone before it has a chance to return to the injection pump (return valve was closed after the bleeding spigot) so the 160 degree water went into each radiant zone and the temp gauge showed 160 before it was exhausted. So I can push 160 degree water into my radiant zones if I bypass the return plumbing. We wanted to be sure we had no blockage in any of the piping and that all of the radiant zones were clean and fresh. With the system in normal operating mode I can get 160 degree water to the radiant manifold (60 feet away) but I cant get it to push or get pulled into the zones with brand new circulator pumps. For some reason it seems to mix with the return water and get stalled at the manifold. There is no manual mixing valve. I have a Taco PC 705-2 variable speed mixing controller that speeds up the injection pump 60 feet away based upon demand, outside temp, heating curves, etc.... I will try bypassing the controller wiring over the weekend to see if it is somehow impeding the flow of the injection pump. If not I believe I am down to a faulty/corroded boiler pump or faulty/corroded injector pump (both are 007-F5s and only two years old). If either becomes the culprit I would be concerned of the replacment longevity.. should I upsize or go with stainless over cast iron.. thoughts?
  • CHRISHALL
    CHRISHALL Member Posts: 9
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    Quicker response to your questions...
    No on strainers
    Great suggestion on bypassing the mixing controller and wiring the injection pump directly - I will try over the weekend.
    All radiant zone pumps are brand new (injection pump and boiler pump are only 2 years old)
    No other devices blocking/impeding flow
    Plumbing flushes cleanly with no restrictive blockages
  • Tom_133
    Tom_133 Member Posts: 893
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    What kind of tubing is your radiant?
    Tom
    Montpelier Vt
  • CHRISHALL
    CHRISHALL Member Posts: 9
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    It's a black rubber tubing labeled...3/8 Onix by Heatway. So this morning I rewired the injection pump to bypass Taco PC 705-2 variable speed mixing control. Instantly the radiant zones rose to 140 degrees. Looks like I am now in the market for a new mixing solution.
  • hot_rod
    hot_rod Member Posts: 22,505
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    If you get temperature the manifold location, but not through the tube? Nothing else has changed? Pumps flowing the proper direction?
    It sure sounds like a air bubble, blockage, or frozen tube

    If you are not getting temperature into the radiant loop, suspect the injection circuit, pump, check, or control not ramping.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • CHRISHALL
    CHRISHALL Member Posts: 9
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    I am now getting 160 degree water into my radiant zones when I bypass the variable speed injection controller wiring. I believe the mixing control setting/wiring or malfunctioning is my problem. I have cleaned up the sensors and now playing with the factory settings on the Taco PC705-2 to see if I can get something to mix between 125-140 or going another route for mixing control. Thanks everyone for your suggestions.. very helpful! Happy Holidays