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Air in One Zone - Could Taco 219 Cause This?

GregBl Member Posts: 16
I have one zone in my system that I can't seem to get the air out of. It's the highest zone. I've bled it multiple times and each time, it works OK and then the air is back. There's no drop in pressure. The expansion tank and pressure relief valve have both been replaced in the last year. (Note - this has been an ongoing problem before and after these replacements.) Could the Taco 219 be trapping air when I do the bleed? Could a bad circulator pump (cavitation) cause this problem? Thanks!


  • Jamie Hall
    Jamie Hall Member Posts: 21,114
    The most important thing to consider when air gets back into a circuit that has been thoroughly purged is... how does it get in? And then to realise that the air can only get in if there is somewhere in the circuit which has a pressure less than atmospheric.

    This is all assuming that it really is bringing in air, and not just little bubbles or gas coming out of solution, which the air eliminator (or whatever kind) should cope with.

    Which leads to... either the system pressure cold is low enough so that at some higher points its actually less than atmospheric, or the pumping is arranged so that near or at the intake to the pump the pressure is less than atmospheric.

    So... what is your cold system pressure? You should have about 0.5 psi for every foot of elevation above the pressure gauge, plus 5 psi. Anything less than that and you could have a problem.

    Then, take a look at the way your pumps are arranged. If they are not set close to the expansion tank but rather are pushing towards it rather than pulling away from it, the pressure at the intake to the pump (and everywhere else in the system) will be less than the cold static tank pressure. In the more extreme cases this can cause cavitation at the pump (which isn't air but water vapour bubbles), but can also allow air to be sucked in near (or at) the pump if the seals are weak but also at high points in the system.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • STEVEusaPA
    STEVEusaPA Member Posts: 6,132
    Also auto air vents and steel expansion tank are another problem.
    Could simply be piping. Even if it's been that way for 50 years.
    Good video about pumping away from the expansion tank:
  • GregBl
    GregBl Member Posts: 16
    Thank you for tge replies. Interesting, the pumps are pushing into the boiler and the outlet of the boiler is where the expansion tank is attached! So, looks like they're turned the wrong way…
  • STEVEusaPA
    STEVEusaPA Member Posts: 6,132
    That would do it as it’s put the top of your system negative.