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Thread: Air bubbles in hydronic in-slab heating system

  1. #1
    DIY Junior Member rmanny's Avatar
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    Default Air bubbles in hydronic in-slab heating system

    Hello - hopefully I've posted this in the right section...

    I have an 8-year old house with radiant heat system in the slab. The system has worked fine for the first 7 winters, but this winter I have new problems.

    The system had been on for several weeks, then started making gurgling noises one night. When I went out to the garage to see what was going on, I could see air bubbles passing through the tubes. I shut the system down immediately.

    My first thought is that I have a leak somewhere, but we've seen no evidence of that.

    The system uses a residential hot water heater to heat the water, has a Honeywell Sparco PV100 air remover valve, and an Amtrol expansion tank.

    There is no pressure guage on the system, so I can't tell how much (if any) pressure is left in the system. When the contractor filled the system originally, he simply attached a hose to the spigot on the bottom of the hot water heater and let the public water pressure fill the system. He then ran the pump, circulating the water and purging the air from each zone. when he was done, he disconnected the hose and the system has been at that pressure ever since.

    I've posted some pics below. Note that there is extra copper piping in some of these pictures because the regular hot water heater in right next to the hydronic heating system.

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  2. #2
    DIY Junior Member rmanny's Avatar
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    This pic might make it a little clearer. I've marked the pipes that are NOT part of the heating system with red arrows.

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    General Engineering Contractor ballvalve's Avatar
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    First suspect is the air valve. But if the heating was working, turn it back on. Water absorbs air quite quickly. wont hur the pump.

    I have an open system and NO air release anywhere. The air was soon gone on its own.

    Why the air relief valve? How would air get into this system? Defeat the valve and try it for awhile.

    Or your amtrol has busted and sent a pile of air into the system.

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    In the Trades Tom Sawyer's Avatar
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    Just re-purge the system. Is that water heater the boiler? If so you will probably have to purge every year or so.
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

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    DIY Junior Member rmanny's Avatar
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    Quote Originally Posted by Tom Sawyer View Post
    Just re-purge the system. Is that water heater the boiler? If so you will probably have to purge every year or so.
    Really? Even though for 7 years never saw this problem? Yes - the water heater is the boiler for the system. What makes you think that the water heater is the culprit?

    I mean, I really want to believe that I can fix this by just filling the system, just want to be sure I'm not going to cause more damage.
    Last edited by rmanny; 12-04-2011 at 08:07 PM.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Air in a system not designed for it damages a system...getting rid of it can't hurt. If there's any seal, seam, etc. that leaks, even a drop over a long time will depleat the system's full state eventually - it doesn't have to even be visible. When things cool off, that very same very small leak might suck in some air as the water shrinks when it cools. Air means oxygen, which means rust or corrosion...you need to get rid of it.
    Jim DeBruycker
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    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    General Engineering Contractor ballvalve's Avatar
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    I have only used water heaters and never have any air. In a plain well tank with no recharge, 30 gallons of air gets absorbed in about a week.

    I think the expansion tank is shot, and thats his first place to look. I dont see any "purge" need. As long as the pump has water when running [unscrew the SS slotted plug at the end] to check, let it run and your air will out on its own.

    Only other incredibly vague chance is a suction air leak before the pump, but it should drip when off.

    http://www.pexsupply.com/Honeywell-S...Air-Eliminator

    This is a manual valve, and it looks like you must lift the lever to get the air out. Have you done that?
    Last edited by ballvalve; 12-05-2011 at 11:01 AM.

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    DIY Junior Member rmanny's Avatar
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    Quote Originally Posted by jadnashua View Post
    Air in a system not designed for it damages a system...getting rid of it can't hurt. If there's any seal, seam, etc. that leaks, even a drop over a long time will depleat the system's full state eventually - it doesn't have to even be visible. When things cool off, that very same very small leak might suck in some air as the water shrinks when it cools. Air means oxygen, which means rust or corrosion...you need to get rid of it.
    Agreed - all the air needs to be purged from the system ASAP. What I am afraid of damage-wise is leak up through the slab into the flooring. I'd like to determine if/where the leak is before re-pressurizing.

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    DIY Junior Member rmanny's Avatar
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    Quote Originally Posted by ballvalve View Post
    I have only used water heaters and never have any air. In a plain well tank with no recharge, 30 gallons of air gets absorbed in about a week.

    I think the expansion tank is shot, and thats his first place to look. I dont see any "purge" need. As long as the pump has water when running [unscrew the SS slotted plug at the end] to check, let it run and your air will out on its own.

    Only other incredibly vague chance is a suction air leak before the pump, but it should drip when off.

    http://www.pexsupply.com/Honeywell-S...Air-Eliminator

    This is a manual valve, and it looks like you must lift the lever to get the air out. Have you done that?
    If you look at the pic I posted of the valve, it looks different than the one you link to. My valve is venting air at all times unless you screw the cap down.

  10. #10
    Retired Defense Industry Engineer jadnashua's Avatar
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    I didn't see a pressure gauge anywhere in the system. Is there one? If not, then you may want to plumb one in, then, it'll be easier to tell if it is leaking. A bad seal on a pump might put air into the system, I think. Maintaining a nominal pressure of maybe an atmosphere or so should help.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    General Engineering Contractor ballvalve's Avatar
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    The valve is the same model number that you posted. I would screw it down and eliminate it. Leaks in a slab dont put air in a pipe it puts water in the slab.

    Have you yet checked the air tank that has a life span of 5 to 7 years, and is full of air?

    that pump has no rotating seal, it is a wet rotor. The only seal is an o-ring at the housing for changing the cartridge, and the flat face seals at the flanges.

    As long as your air bubbles are small, and the pump gets mostly water, it will soon churn the air into the water. I would also open a valve somewhere in the system and flush out the 7 year old water if its closed system. If its closed, what is your make up water valving?
    Last edited by ballvalve; 12-06-2011 at 08:56 AM.

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