air locked radiator

Discussion in 'HVAC Heating & Cooling' started by plaza500, Dec 18, 2009.

  1. plaza500

    plaza500 DIY Member

    Messages:
    35
    Location:
    Canada
    the rad in my daughters room (hot water - 1950) keeps airlocking, her room is on the top floor, only two heaters on the top floor. the other one does not airlock. i have to bleed her heater every couple of days and soometimes she wakes up at 2 am and her room is cold and cries.

    how do i stop the constant airlocking?
  2. nhmaster

    nhmaster Master Plumber

    Messages:
    3,189
    Location:
    S. Maine
    Bump the boiler pressure up about 5 lbs or so. Do not exceed 25 lbs though.
  3. plaza500

    plaza500 DIY Member

    Messages:
    35
    Location:
    Canada
    hmmm... just checked and i'm currently running at 29 (unless the guage is off - it is cracked and yellowed)

    don"t really want to increase it from there though
  4. nhmaster

    nhmaster Master Plumber

    Messages:
    3,189
    Location:
    S. Maine
    I'd bet the gauge is off. The relief valve lets go at 30 lbs.
  5. plaza500

    plaza500 DIY Member

    Messages:
    35
    Location:
    Canada
    hmm.. will get that changed.

    on a side note, there is what seems to be an overflow tube off the furnace that has a bucket under it and most times it is empty, but then i will go downstairs and see the cat drinking out of it and find the bucket full.

    could this be related? i don;t know squat about furnaces
  6. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,059
    Location:
    New England
    You may have a bad expansion tank. Depending on the age and configuration of the system, it may be a bladder tank, and those wear out periodically. The tank could be waterlogged, so when the boiler is on, there's no place for the hotter, less dense water to go, so it goes out the pressure relief valve.
    Last edited: Dec 22, 2009
  7. plaza500

    plaza500 DIY Member

    Messages:
    35
    Location:
    Canada
    would draining the expansion tank help?
  8. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,059
    Location:
    New England
    There are two types of expansion tank generally available. Most modern systems use a bladder type tank. When these fail, they fill up with water and no longer work. The older style were just a big tank with a special air valve. These aren't anywhere near as good since you always are adding air to the water since there's no bladder or barrier between the two. Air in a boiler system is not good. This is more often used in a well/pump water supply system. If the bladder tank is shot, you must replace it. They have a schrader valve on the bottom (just like your tire). If you try to take the pressure, if it is shot, you'll get water out. It normally isn't full of water and should sound hollow if you tap on it. If you don't get water out, it may have a leaky valve and lost its air. To pressurize it, you need to relieve the water pressure before you can add air.
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