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  1. #1
    Join Date
    Feb 2008
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    Default Expansion tank quick-fill knob - open or closed?

    I'm sorry to make my first post a request for help, but I hope someone can take pity on a slightly overwhelmed first-time homeowner.

    I have an Amtrol Extrol 2 gallon expansion tank for my gas furnace. It is connected to (or in series with, if it were an electrical diagram) both a valve that turns water to the tank on and off, and something called a quick-fill knob.
    My question is about that knob. After bleeding the radiators (a necessity it seems after having someone replace the flame sensor), I opened the valve and turned the quick-fill knob to 'open' to increase the water pressure back to 12psi or so. But now I'm not sure if that quick-fill knob, which doesn't start water flowing into the tank on its own, should be turned to open or closed after reaching normal pressure. I can't remember if I actually turned it to 'open', or it was like that already. I ask because the water pressure got very high last night after the flame sensor was replaced, to the point where the pressure relief valve was needed (30+ psi).

    So, should that knob be turned to open or closed? Is this even relevant in light of the pressure increase?
    Last edited by jhgoldstj; 02-05-2008 at 10:26 AM. Reason: clarity

  2. #2
    Join Date
    Aug 2007
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    443

    Default Re: Expansion tank quick-fill knob - open or closed?

    As I understand this unit, it is known as an Amtrol Fill-trol system and has an automatic fill valve which is actuated by the diaphragm pressure in the expansion tank, which is pre-set at 12 psi.

    It is designed to allow more water into the the piping/boiler system when the pressure falls below the 12 psi.

    If you have an on/off knob on the Fill-Trol, try turning it to close.

    Place a bucket under the Pressure Relief valve & temporarily open the PRV valve to get the gauge pressure back to 12 psi.

    If you have an on/off water shutoff valve that supplies the cold water from the house to the system, turn THAT off as well & watch the gauge to see if the psi stays between 12 psi and 20 psi (hot water expands 5% when heated, so there will be SOME increase in pressure as the system heats).

    If the system continues to hover around 30 psi & the PRV continues to open & spill water, chances are the internal bladder of the expansion tank has sprung a leak.

    There is a simple way to check the expansion tank, so post back if you have a continued problem.
    Last edited by JacktheShack; 02-05-2008 at 12:58 PM.

  3. #3
    Join Date
    Feb 2008
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    6

    Default Re: Expansion tank quick-fill knob - open or closed?

    Thanks so much for the info. Sounds like something I can actually do, which is a relief. This morning before work I actually did a short test similar to what you suggest; I let the furnace run for about an hour after getting the psi back to 12. During that time, the psi rose to around 18 (or at least not 20). It seemed to climb fairly steadily throughout the hour. I had to leave for work, and decided to turn the thermostat to off. After about 5 minutes, the psi read 15 again. Does any of that seem out of order to you? I'll be sure to do a longer test this evening.

  4. #4
    Join Date
    Aug 2007
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    443

    Default Re: Expansion tank quick-fill knob - open or closed?

    jh****sj:

    Those psi parameters are normal.

    As noted, boiler water always expands 5%, so cold boiler water should read ~12 psi; hot boiler water should read up to ~20 psi, then go back down to 12 psi again when it cools & loses volume.

    Don't expect the gauge needle to point directly to 12 or 20; changing atmospheric conditions & how high the water is heated under various heat loads varies during the day & have an effect on what the gauge needle says.

    The flexible neophrene bladder inside the expansion tank acts like a coiled spring to absorb the heated, expanded water during the heating cycle.

    Keep a pail under the pressure relief valve for the time being.

    Post back if you have a problem.

    Google "Amtrol Fill-Trol system", or "Fill-Trol" (without the quotation marks) to get various sites for more info on how the Fill-trol works.
    Last edited by JacktheShack; 02-05-2008 at 03:04 PM.

  5. #5
    Join Date
    Feb 2008
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    6

    Default Re: Expansion tank quick-fill knob - open or closed?

    ***, thanks again. It's a relief to hear about the psi changes. I'll definitely write back if things get out of whack again. But since I'm here, would you mind taking a guess as to why the pressure went so high after getting a new flame sensor? Are they even related? The only things different I noticed after the replacement was that the pilot flame seemed more robust than the old flame, and the damper on the chimney was left on 'open' instead of 'automatic' (or similar terms) by the technician. Could either of those be the culprit? Could it just be that once a pilot light goes out one should bleed the radiators again?

  6. #6
    Join Date
    Aug 2007
    Posts
    443

    Default Re: Expansion tank quick-fill knob - open or closed?

    jh****sj:

    I haven't a clue!

    Neither changing the flame sensor or the damper setting should have any effect on boiler water volume.

    It's quite normal for a tech to check out different parts of the system, sometimes just for curiosity, or to make sure he/she remembers how they work.

    The Fill-Trol is nowhere near as common as the Extrol expansion tank, which is extremely common on hydronic systems, & is always combined with a pressure reducing valve that maintains incoming water pressure at the standard 12 psi.

    The tech may have simply twirled the knob on the Fill-Trol to see how it worked.

    That's MY best guess.

    There is no need to bleed the system of air now unless you hear air noises inside the pipes when the hot water is circulating.
    Last edited by JacktheShack; 02-05-2008 at 03:42 PM.

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