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psi dropped, no signs of water leaking

BoonBoon Posts: 226Member
I can't believe I'm about to be this guy. I swear there are no leaks! Both the wife and I checked for leaks many times - like crazed maniacs, I'll add. All my work is still exposed and there is no sign of water leaking, no rust spots, no damp spots, no pipes under slabs, all exposed, nothing. There is only 1 auto air vent above the expansion tank, and I'm pumping away. All the other air vents are manual.

System psi was at zero when I walked by it today. I barely had to add any water to bring it up to 15psi. The system has been running for like 6+ weeks and at temps as high as 165. Every time I notice the gauge at the expansion tank, it hasn't been below 15psi. Over the last week+ I did notice [heard] some air accumulating in a couple second floor radiators.

This same type of thing happened to me just 2-3 weeks after commissioning the system so I'm hoping someone will tell me that I just did a poor job of removing the air when I commissioned the system, and that after it ran for a while - and at higher temps - air gradually came around, hit a vent, and the pressure drops. I'd like to think that is what I'm seeing here. Is this theory a dream or possibility?

DIY'er ... ripped out a perfectly good forced-air furnace and replaced it with hot water & radiators.

Comments

  • GWGW Posts: 3,071Member
    It's a ghost, a leak, or an air pocket, or the expansion tank needs some scrutiny.

    I'd start at idea #4 and work backwards

    Gary
    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
    www.wilsonph.com
    [email protected]
  • BoonBoon Posts: 226Member
    I like my chances that it isn't a ghost. I shall scrutinize the paint off of that tank... I tapped on it earlier today out of frustration but didn't think to listen to it. Thanks.
    DIY'er ... ripped out a perfectly good forced-air furnace and replaced it with hot water & radiators.
  • hot rod_7hot rod_7 Posts: 9,030Member
    Any time air vents out the pressure will drop. I assume you do not have an open fill valve or fill tank?

    I prefer to keep one of those open and operating for a few weeks after a system first starts.

    You have a good central air scrubber, is it working?

    If you hear air in the upper portions, you haven't scrubbed all the micro bubbles out, yet.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • BoonBoon Posts: 226Member
    I closed the fill valve a few days after starting the system.

    I have a spirovent above the exp tank. And I now remembers that I have a spirovent on the buffer tank, too, and there are also air vents on the Caleffi manifolds. How could I forget about 5 other vents?!

    Off-topic PS I love those manifolds, the fostapex prep tool hack worked perfectly, the flare nut wrench was worth every penny, and every connection was perfect the first time.
    DIY'er ... ripped out a perfectly good forced-air furnace and replaced it with hot water & radiators.
  • hot rod_7hot rod_7 Posts: 9,030Member
    The panel rads should have manual vents on them also. That is the "final frontier" for air to hide usually the highest points in a system. Run the system up to 180, do a good manual purge at each radiator and you should be done.

    Fill pressure set to assure + 5 psi at the highest point in the system? Highest point above the fill point X .433 + 5

    So 20 feet of elevation 20 X .433 + 5 = 14.66 psi fill. Confirm with an accurate pressure gauge, boiler supplied gauges are not often that :)

    That positive 5 helps remove troublesome air bubbles also. If your pressure drops below that, small air bubbles collect and linger at those upper points in the system.

    Spiro vent at the hottest point in the system, right at the boiler discharge. Expansion tank at the inlet of the boiler circulator, that is not always one and the same.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • Solid_Fuel_ManSolid_Fuel_Man Posts: 1,196Member
    I've had that happen as well. Commissioned system everything hot and shut off prv a few days later. System all good, get a call several weeks later saying funny noise in mechanical room. Pressure reads 0. Very little water to bring pressure back up.

    When you think about it, on a warm system we don't have much cushion in that expansion tank if it's 2psi below full pressure. Only a small volume of water is in that expansion tank, as we want to get the most usable volume out of it.

    I find on wood fired systems which can see occasional Temps near boiling that air will still burp out on that first near boil, even after the system has been running many months.

    Taylor
    Master electrician specialising in boiler and burner controls, multiple fuel systems, radiant system controls, building controls, and universal refrigeration tech.
  • hot rod_7hot rod_7 Posts: 9,030Member
    I find on wood fired systems which can see occasional Temps near boiling that air will still burp out on that first near boil, even after the system has been running many months.

    Exactly, here is what that might look like. A layer of micro bubbles is formed every time the fire is in contact with the HX surface.






    Another cause of micro bubble formation is cavitation. Commonly experienced at a pump impeller but it can be induced at highly throttled valves or other flow restrictions.

    As the water temperature increases it becomes easier to coax this condition.





    Here is a spec sheet from a Grundfos Alpha, notice the required minimum pressure as temperature increases.





    I suspect many of the wood burners that have experienced operating conditions above 200F, may experience reoccurring air and possible pump cavitation issues. Pumping away is critical in those high operating temperature systems.

    It becomes clear why open sytem OWF type systems suffer frequent pump failures :)
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • Solid_Fuel_ManSolid_Fuel_Man Posts: 1,196Member
    @hot rod you always have the cool graphics and idronics to show! One of my favorite reading materials is idronics. The industry would really change if all "professionals" read idronics, and Dan's "pumping away". These concepts of thermodynamics and basic hydronic science makes it blatantly obvious how to sold so many common problems, which shouldn't exist from day one.
    Master electrician specialising in boiler and burner controls, multiple fuel systems, radiant system controls, building controls, and universal refrigeration tech.
  • j a_2j a_2 Posts: 1,795Member
    Did by chance you add an inhibitor...Does the circulator match your system. Are you using coin vents or manual vents....Did you ever preform a hydrostatic test....
  • Solid_Fuel_ManSolid_Fuel_Man Posts: 1,196Member
    @hot rod OWF and open systems....neither one are high on my list of likes.
    Master electrician specialising in boiler and burner controls, multiple fuel systems, radiant system controls, building controls, and universal refrigeration tech.
  • BoonBoon Posts: 226Member
    @j a I tested to 50psi, no additives, circ is a good match, I think, and I have a mix of vents. I'm pretty sure the drop is from a hasty commissioning. I'm tempted to add some dish soap after I add the next 5 radiators.
    DIY'er ... ripped out a perfectly good forced-air furnace and replaced it with hot water & radiators.
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