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Air in zone or circulator pump????

Hello there, new guy here. Looking for help from the pros!
I recently extended a zone on my hydronic heat system and when I went to turn the zone back on and test the heat and it came up very slowly. 
I have an air purge valve at the highest point of the system that I hear venting. 

The circulator turns on like I’d normally expect. 
When I purge the zone manually the water doesn’t come rushing out full pressure when I open the drain valve. 

This is the first time I’ve tested the heat since last spring. 
Am I looking at a fresh water feed valve or circulator pump issue??? 


  • STEVEusaPA
    STEVEusaPA Member Posts: 5,872
    Why would it be your circulator?
    You need to keep the pressure up around 20 psig while purging.
  • hot_rod
    hot_rod Member Posts: 17,510
    Sounds like an airlock in the piping. Got a drawing of how you purged it?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Zman
    Zman Member Posts: 7,405
    The funny thing about auto vents on the top of the system is that air being sucked in sounds a lot like venting.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • woodpecker49
    woodpecker49 Member Posts: 3
    Hot rod,
    Thanks for the reply. 
    See drawing and pic. 
    I opened both valves in zone loop and closed the valve that’s between drain and boiler return. (I additionally closed the valves in the second zone to isolate the purge)

    When I open the drain valve water doesn’t come rushing out like I expected. Even with circulator on. Water does drain out but very slow and eventually stops. 

    The more I’m thinking about it I’m convinced the fresh water feed valve is sticking. I’ve read that those valves fail regularly and some boiler guys change them out regardless when changing circulator. I’m not sure exactly how the feed valve should work but the little lever on the body won’t swing, but if I press it downward with some force I can hear water moving. 

    The valves are available at Home Depot so I’m gonna change that this morning. I’ll update with progress. Curious if you have the same conclusion or see something I don’t. 

    I appreciate the help!
  • HomerJSmith
    HomerJSmith Member Posts: 1,799
    Although pressure and flow are related, flow is the most important part. One needs a flow rate of 2'/sec to remove air from an air bound sys loop. I don't think that you have that if you purge thru the fill valve, which is why one sees a lot of boiler fill valves with a by-pass that allows street pressure and flow around the fill valve. I see so many sys that lack isolation and purge valving which makes it more difficult to get the air out.
  • hot_rod
    hot_rod Member Posts: 17,510
    Best to replace the fill valve. they often stick and over-fill if they sat un-opened for years, not worth the risk.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • woodpecker49
    woodpecker49 Member Posts: 3
    Fill valve did it! 
    Purged a few buckets till no bubbles and heat came right up. 
    Thanks for the help!