Hydronic Low Water Cutoff Issue
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  1. #1
    Join Date
    Mar 2009
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    7

    Hydronic Low Water Cutoff Issue

    Problem: (system particulars below) In zoned system, first floor is heated w/in-slab tubes, upstairs by baseboard radiators (normally not run as we don't use the second floor for much). Unless air is periodically removed from system by running upstairs baseboard radiators, low water cutoff shows a yellow warning light and cuts blower off while tank gets up to temperature. It will restart quickly, run a few seconds, then get cut off again, and repeats this until the tank is up to temp.

    The problem started after the system had been in place for several years. Low water cut-off is mounted high so light cannot be seen when standing, unless you're elevated or unless you put a finger behind the light and get the reflected glow. First two techs replaced the Aquastat which seemed to work for a while, though at great expense.

    Third tech was about to replace the Aquastat and happened to see the Low Water Cut-off light. He suggested bleeding the air from the system by running the upstairs zones (normally closed) and that worked. He had no suggestions for why this needed to be done or why the air was accumulating in the closed zones, or how the problem could be prevented.

    At this point, we have to run the upstairs zones for an hour or so every 2-3 weeks (when we notice the system clicking on/off).

    Anyone know of a firm fix for this issue? Is something waterlogged (e.g. the expansion tank)? System particulars below. Any info appreciated.

    System (11 years old):

    Buderus Boiler G115 w/Becker blower, on top of integrated Buderus hot water heater

    Amtrol Extrol Expansion Tank for Hydronic Heat Systems, Model 30 (pre-charge 12 psi, max 100 psi, temp max 240)

    Honeywell Aquasat (3-4 years old)

  2. #2
    Join Date
    Mar 2009
    Posts
    4
    do u have zone valves or pumps and is the boiler actually low on water? Have they ever pulled the low water cutout ot see if its plugged or dirty

  3. #3
    Join Date
    Mar 2009
    Posts
    7
    Quote Originally Posted by JoDU View Post
    do u have zone valves or pumps and is the boiler actually low on water? Have they ever pulled the low water cutout ot see if its plugged or dirty
    1. Zone Valves - Yes - there are thermostat-activated valves for the larger zones, and the zones downstairs (slab tubes) have individual twist on/off valves to regulate the zones more specifically. We've never messed with those valves, and the thermostats are functioning. There are 3 pumps.

    2. Boiler Water Level - So far as I know, the techs did not check it, and I do not know how to check it (but would like to, but also don't want to run afoul of the "No DIY" policy). One tech did say, "if the system was low on water, the Low Water Cutout light would not go out."

    3. Pulling Low Water Cutout - So far as I know, the techs did not pull the Cutout to check it. Again, I be happy to, but don't know how. All I know for sure is that running the upstairs zones temporarily cures the problem (Low Water light goes out).

    4. There are 3 BB tubes upstairs, each has a vent, one of them has a screw-on top that was allowing a small amount of water to burble out around the top (not out the appropriate vent hole), suggesting that air could be being sucked into the system.

    Perhaps you could point me to some form of manual or other resource for performing these checks? And where I could get replacement vents. Thanks for your questions - they're helpful.
    Last edited by Equito; 03-09-2009 at 08:32 PM.

  4. #4
    Join Date
    Dec 2007
    Posts
    4,665
    pictures of the boiler showing the location of the controls, pumps, etc.

  5. #5
    Join Date
    Jul 2000
    Location
    Northern Wisconsin
    Posts
    1,962
    What information can you give on the type of tubing that was used for the infloor heating on the main floor? Brand? Any markings/specs printed on it?
    Use the biggest hammer you like, pounding a square peg into a round hole does not equal a proper fit.

  6. #6
    Join Date
    Feb 2008
    Location
    Altmar, New York, United States
    Posts
    4,119
    Quote Originally Posted by Equito View Post
    Problem: (system particulars below) In zoned system, first floor is heated w/in-slab tubes, upstairs by baseboard radiators (normally not run as we don't use the second floor for much). Unless air is periodically removed from system by running upstairs baseboard radiators, low water cutoff shows a yellow warning light and cuts blower off while tank gets up to temperature. It will restart quickly, run a few seconds, then get cut off again, and repeats this until the tank is up to temp.

    The problem started after the system had been in place for several years. Low water cut-off is mounted high so light cannot be seen when standing, unless you're elevated or unless you put a finger behind the light and get the reflected glow. First two techs replaced the Aquastat which seemed to work for a while, though at great expense.

    Third tech was about to replace the Aquastat and happened to see the Low Water Cut-off light. He suggested bleeding the air from the system by running the upstairs zones (normally closed) and that worked. He had no suggestions for why this needed to be done or why the air was accumulating in the closed zones, or how the problem could be prevented.

    At this point, we have to run the upstairs zones for an hour or so every 2-3 weeks (when we notice the system clicking on/off).

    Anyone know of a firm fix for this issue? Is something waterlogged (e.g. the expansion tank)? System particulars below. Any info appreciated.

    System (11 years old):

    Buderus Boiler G115 w/Becker blower, on top of integrated Buderus hot water heater

    Amtrol Extrol Expansion Tank for Hydronic Heat Systems, Model 30 (pre-charge 12 psi, max 100 psi, temp max 240)

    Honeywell Aquasat (3-4 years old)
    did they use tape or pipe dope on the threads? sometimes tape will rip and cause a screwy situation with the ground. i have had this happen a few times.

  7. #7
    Join Date
    May 2000
    Location
    Urbandale IA. USA
    Posts
    4,881
    If you have a combination of galvanized/steel pipes and copper, you can get electrolosis between the pipes (like a battery).
    Mineral salts in the water which normaly corrode pipes, then act like an electrolyte and the water in the system decomposes into hydrogen forming vapors in the system...
    Those who dance, appear insane to those who do not hear the music.
    Those who believe, appear ignorant to those who do not know God.

  8. #8
    Join Date
    Mar 2009
    Posts
    7
    Here are some pics of the very tight install.



















    1. The pipes in the slab are copper, but that's all I know about them.

    2. I can see tape on some of the joints (bigger pipes).

    3. I checked the air purge valves on the upstairs baseboards. All but one have a recessed slot in the top (photo 2396, below), and the remaining one (photo 2392, below) looks like a Hygrometer-style (larger screw-on top that also has a slot, though more flush with the top).





    The Hygrometer-style leaked a little water around the top (beneath the top ring), but not out the bleed hole, when I rocked it with finger pressure. I tightened up the top ring and it stopped. Not sure if there are those fiber disks in there, or not.

    Thanks for the input.

  9. #9
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,616
    The air eliminator is probably dirty, and not working.

    And they left no room to get to it and clean it.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  10. #10
    Join Date
    Mar 2009
    Posts
    7
    Quote Originally Posted by beenthere View Post
    The air eliminator is probably dirty, and not working.

    And they left no room to get to it and clean it.
    1. Is the air eliminator the vent thing seen in the 6th pic down, just to the right side of the red cutoff valve that has a pipe coming from the bottom and going over to the Extrol unit?

    That vent is where the air comes out once you run the upstairs baseboards.

    If the air eliminator is somewhere else, please let me know where it's likely to be, and what it looks like, as the wall to the left of the unit is removeable and I may be able to get to it.

    Thx

  11. #11
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,616
    That would be the air eliminator.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  12. #12
    Join Date
    Jun 2006
    Location
    New Jersey
    Posts
    4,325
    Copper in the slab may be leaking. You constantly are requiring make up water, which is bringing oxygen. The spirovent in either dirty or clogged. The baseboard returns coming off the top of the return, provide a nice place for the oxygen to go. Also for your picture, I can't see how the mixing valve or diverter valves is able to work properly, piped that way.

    If you are purging air, then where is it coming from. Best guess, the make up water from a leak or leaks in the slab.

  13. #13
    Join Date
    Mar 2009
    Posts
    7
    Quote Originally Posted by ascj View Post
    Copper in the slab may be leaking. You constantly are requiring make up water, which is bringing oxygen. The spirovent in either dirty or clogged. The baseboard returns coming off the top of the return, provide a nice place for the oxygen to go. Also for your picture, I can't see how the mixing valve or diverter valves is able to work properly, piped that way.

    If you are purging air, then where is it coming from. Best guess, the make up water from a leak or leaks in the slab.
    I like the sound of "your baseboard air purge vents are allowing air into the system and need to be replaced" a WHOLE lot better than "your slab-bound copper tubes are leaking."

    The main vent does let air out (you can hear it), but only when the upstairs is brought into play.

    If there was a leak in the slab tubes requiring water to be replaced, why wouldn't the make-up system just do it on its own, without the upstairs baseboards being activated? It seems the make-up system would prevent the Low Water Cut-off from activating and killing the burner.

    If the make-up system isn't functioning normally, then why would it do so when the baseboards are activated?

    I'm starting to understand the complexities of this system, so that's a start. I just want to have an efficient conversation with my tech, so this is all good info.

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