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Two zones heating issue...

Skyline
Skyline Member Posts: 154
in Gas Heating
My heating system has two zones, one is with CI radiators, while the other is baseboard. This works just fine most of the times, but it is dependent on which zone starts up first. Here's an image for the circulators and the spiro vent:



The issue in a nutshell...

Zone #2 starts up without zone #1 being active, it works just fine. When the zone #1 starts after zone #2 is active, the circulator light for zone #1 blinks blue, indicating air in the pump. Seemingly, the time delay for zone #1 start up plays a role in this; the longer it is, the more likely that the zone #1 circulator gets air in the pump.

Resolving this requires shutting off the thermostats for both zones, turn on the thermostat for zone #1, wait until the circulator pushes out the air and then, turn on the thermostat in zone #2 to have both zones running. When only zone #1 active initially, there's some gurgling noise coming from the boiler for a short time.

Reversing the start up order, #1 and then #2, there are no issues; both circulators run just fine, no gurgling noise in the zones and/or the boiler.

What is the cause of this issue and how can it be remediated?

TIA...

Comments

  • Zman
    Zman Member Posts: 7,611
    A picture from farther back would help. Where is the expansion tank located?
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Skyline
    Skyline Member Posts: 154
    The expansion tank is connected to the spiro vent and also to the water pressure regulator for the heating system:



    In 4' x 5' boiler room, it's not easy to take a picture far away...
  • Zman
    Zman Member Posts: 7,611
    edited December 2020
    What system pressure are you running? Does the issue get better if you raise the pressure? Which zone is the cast iron on? Is it an old gravity system? Does throttling the valve after the circ change anything? Are there check valves on the zones?
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Skyline
    Skyline Member Posts: 154
    @Zman thank you for your help..

    The system pressure is between 12-14 PSI, haven't tried to raise the pressure yet.

    Zone #1 is the CI radiator.

    No old gravity system, circulators in boiler and for the zones.

    The checkvalves are builtin to the circulators, will try throttling the valve after the circulator...
  • rick in Alaska
    rick in Alaska Member Posts: 1,466
    Try holding your hand on the pipe going to zone one and see if the temperature changes when zone two starts up. Leave zone one off for this test. It could be the check valve in zone one is stuck open.
    Rick
    Zman
  • Skyline
    Skyline Member Posts: 154
    Thanks @rick in Alaska ...

    The checkvalve is built-in to both of the circulators.

    I did test the temperature before and after (pressure side) for the #1 circulator. Before the circulator it is warm, while after the circulator it is cold.

    This is the time, when the circulator alternatively blinks blue and orange lights. The manual states, that the blinking lights means cavitating/has air bubbles on the sucktion side and cannot open the checkvalve. Remediating this issue requires releasing the air bubbles.

    Shutting off zone #2 circulator increases the water pressure in the manifold, that helps openning up the checkvalve in the #1 circulator. I can hear the air gurgling through the pipes, boiler and removed with the spiro vent. It does not take long, once it gets going.

    I just don't know from where this air gets in to the manifold?

    It seemingly coming from zone #1, maybe it has a leak somewhere, but I don't see it. The basboard in zone #2 is pretty much the lowest point in the heating system, air bubble probably would not accumulate there.

    Alternatively...

    Is it possible, that the #1 circulator being hot on one and cold on the other side causes some bubbles that builds up on the sucktion side?

    When zone #1 calls for heat, maybe there are enough bubbles, that prevents openning the checkvalve. As mentioned in the OP, the longer it takes for zone #1 to call for heat, with #2 already running, the more likely this issue shows up.

    The reverse start up, #1 and then #2 circulator, has no issues regardless when #2 starts up...



  • Zman
    Zman Member Posts: 7,611
    That's a puzzler.
    Pull the circ and inspect the impeller and check valve?
    Check that the air sep is not plugged?
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Skyline
    Skyline Member Posts: 154
    @Zman...

    As a home owner, I don't like puzzler and pretty certain, that neither do plumbers, especially when it comes to heating systems...

    Both circulators are about three month old. While I understand, that it doesn't mean much, as far as quality of the circulator is concerned...

    Why would this issue only show up, if zone #2 starts up first? If there's some problems with #1 circulator, why this issue is not there, when #1 circulator starts up first?

    It's pretty much the same for the spiro vent. Why would the order of zones start up impact it's operation? This vent either works, or doesn't, no?

    Maybe your original suggestion for remediating this issue was spot on, increase the system pressure.

    I have no clue how to do that; off to find the brand, model # and a manual on the web...





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