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pressure lose with a clue, maybe?

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PDB2
PDB2 Member Posts: 26
This is a fairly small simple 2 zone baseboard system that loses pressure to 0psi, but only when the boiler is inactive and has cooled for a few hours. If the weather is such that it is actively cycling ..no problem. I've scoured the system looking for any obvious water loss. There is only about 20' of baseboard circuit I can't get a visual on, but I would think any leak there would eventually show up in surrounding sheet rock. I did shut the system down a couple weeks ago to check pressure tank. It was only reading 6psi so recharged to 12, but that didn't seem to solve anything. I've added very small amounts of water 3 or 4 times since then to bring pressure back. Could I still be purging air? My close boiler piping is valved such that I only drain 1/2 gallon or so to check tank pressure, so would that be reasonable?
So anyway, is the cold boiler condition a useful clue?

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  • Jamie Hall
    Jamie Hall Member Posts: 23,635
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    A hot water system should not lose any pressure for months -- or years -- at a time.

    That said, how come you have to shut the system down and lose half a gallon of water (which will drop the pressure for sure) to check the pressure in the system? That's not piped and valved correctly, and needs to be fixed. Pictures? Or better yet, pictures and a diagram?
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • GroundUp
    GroundUp Member Posts: 1,955
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    Assuming you're draining the water side of the expansion tank to zero before testing the air side (it sounds like that's the case), I would have to think your expansion tank is too small. If you set the cold static fill pressure to 12 psi to match the air side, what happens when the boiler heats up? Does the pressure spike?

    Where is your system circulator in relation to the air eliminator and expansion tank? Where is the pressure gauge in relation to the system circulator? There are a multitude of possibilities here, but I don't think a leak is one of them if it's not visible to you.
  • PDB2
    PDB2 Member Posts: 26
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    The system didn't lose any pressure for years.

    I shut the system down to check bladder pressure because I wasn't seeing 12 lbs. cold pressure.I isolated and drained the water side of the bladder, about half gallon . I was able to isolate the pressure tank using the valves I have in piping.

    After recharging the bladder to 12 lbs.(it only had 6) I only needed to add about a half gallon of water back into the system to get back up and running.
    When the boiler heats the pressure only gains 3-4 lbs.

    There are 2 circulators, one on each zone. They are after the pressure tank/air eliminator, boiler output side. The pressure/temp gauge located as first thing output side of the boiler.

    I was assuming that with a service refill you could expect to have to add some water as any air elimination occurs for a while. That's why I detailed how much water I lost to be able to recharge the bladder with no pressure on the water side of the pressure tank.
    I hope it's a little clearer maybe?

    It's a Weil McClain CGa-3 59k btu output.
    I calculate water amount for system to be 8-9 gallons total. The pressure tank is 2 gal amtrol fil-tron. I've never seen any pressure above 15psi hot.
  • Big Ed_4
    Big Ed_4 Member Posts: 2,827
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    Yes you need to set the charge of the tank to the dirsired pressure with a open hose when you have a fill tron ..To check for any leaks . Shut off the valve before the fill tron . and see if pressure drops ... Look for where the pipes cross under a slab .

    There was an error rendering this rich post.

  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,829
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    Sounds like an expansion tank problem
  • PDB2
    PDB2 Member Posts: 26
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    I had ordered a tank and it came today. It was my initial thought as well, but was curious if anyone had any thoughts as to why pressure would hold if boiler was actively cycling .
    I'll post results after I get new tank installed. Thanks all
  • GroundUp
    GroundUp Member Posts: 1,955
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    After you charged the air side of the tank to 12 PSI, how many PSI did you charge the water side to? If there was 6 PSI of air in the bladder of the tank it's highly unlikely that there is a tank issue unless it's undersized or your gauge was reading incorrectly. A bad bladder would've had water in the air side and no air. The cold and hot pressure should stay the same with a properly charged and sized tank. Do you have another pressure gauge to check the new tank with and verify both gauges read the same? I just ran into this a few months ago on a big commercial job where my tire gauge was reading extremely low which caused pressure spiking on heating. A new gauge (actually two) had me bring the pressure down to what was only 4psi on the original gauge which fixed the spiking issue.
  • Big Ed_4
    Big Ed_4 Member Posts: 2,827
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    He said he had a Amtrol Fill-trol .. You set the system pressure by the air pressure in the tank . You may not have seen one .They are not commonly seen , around me anyway ..

    There was an error rendering this rich post.

    GroundUp
  • BillyO
    BillyO Member Posts: 277
    edited April 2020
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    get rid of the fill trol and put extrol tank and fill valve.