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Hydronic boiler system won't circulate

bgould5bgould5 Posts: 5Member
Hi everyone,
I have a single zone system in a house that suffered a freeze up and sat vacant for years. I repaired every break in the house plumbing and most all of the ancillary stuff on the boiler (circulator pump, purge valve, etc). The boiler fires up and I have domestic hot water, however, I either can't get the system bled of air properly, or something is preventing the system from circulating hot water. It seems strangely plumbed to me, and I am thinking about cutting in a ball valve and spigot just above the circulator to ease in bleeding the system. I have bled air out of both the two radiators that have bleeder screws, as well as two spigots on the return, located just upstream of a 'thrush balancer' about 12 feet from the boiler. This one's got me confused. Pics coming and thanks in advance for any help!


  • bgould5bgould5 Posts: 5Member
    Two pics show the plumbing at the boiler. The other shows the 'thrush balancer' and one shut off, located away from the boiler. Let's see, what else can I add. This heats the second floor. The new tridicator indicates 18 pounds of pressure and I get a good spray at the bleeder valves, so the water is getting up there fine.
  • bgould5bgould5 Posts: 5Member
    Sorry for the clunky way of inserting pics. Happy to provide more if that would help.
  • bgould5bgould5 Posts: 5Member
    One more thought- can a bad expansion tank lead to a situation like this, where air is being sucked in by the tank to the system won't circulate?
  • GordyGordy Posts: 9,264Member
    Not trying to be smart, but the circulator is wired now to the boiler controls?
  • ZmanZman Posts: 4,895Member
    I would start with the circulator. Does is have voltage? Is it drawing amps? Are the isolation valves open? Can you hear water/air moving?
    I cannot tell from your pictures what your bleeding technique should be. You need to close a valve somewhere in the near boiler piping then push water in one end and pull it out on the opposite end. The path needs to to include the boiler and the radiators
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • STEVEusaPASTEVEusaPA Posts: 2,918Member
    bgould5 said:

    One more thought- can a bad expansion tank lead to a situation like this, where air is being sucked in by the tank to the system won't circulate?

    No, never.

  • bgould5bgould5 Posts: 5Member
    Zman, your description of how bleeding out air is supposed to work is very helpful. The circulator is getting voltage and running. I have even verified this by removing the motor and watching the impeller move under power. The only valve in the whole system is on the outbound side of the boiler, past the expansion tank, out 12' from where water exits the boiler on it's way to the radiators. There are two spigots on the return line, both about 12' before the circulator and boiler. I could hear air escaping from the system as I opened the bleeders on the radiators, which I did with the circulator off, but I don't sense any movement with the system closed up and the boiler and circulator on. If I crack a spigot on the return line, I can feel the length of pipe between it and boiler get warm, but nowhere else. It seems this would indicate water flowing the opposite direction that it's supposed to. Is the circulator the only thing in a hydronic system that controls the direction of water? Is there anything in the boiler itself that plays a role, like a one way valve? I assume when I open the system, water pressure from the street is compensating, making the hot water travel the path of least resistance, those 12' to the open line instead of the much longer path through the radiators.
  • ZmanZman Posts: 4,895Member
    Is there an isolation valve on your circulators flange. It looks like a drip is coming from a valve that you would turn with a screwdriver.
    Did that circulator freeze? If the impeller froze, i could have separated from the shaft.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • DZoroDZoro Posts: 761Member
    Put in new isolation flanges with fill/purge valves on them. Then you can get a full system purge with water using those valves. The air vent above the circulator isn't in a good location the cap on it really should be tight. It could actually suck air in with it's location to the pump. Like Zman said check the pump propeller/shaft carefully.
  • HVACNUTHVACNUT Posts: 2,184Member
    In your first pic with the drain and the valves. Is that the return?
    If so the opposite side of that tee valve should also have a drain.
    They look like 1/4 turn valves.
    You need to purge them separately.
    Close off one side, purge the other side, then switch.
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