Boiler water pressure too high ...

Discussion in 'HVAC Heating & Cooling' started by jgraves, Feb 8, 2011.

  1. jgraves

    jgraves New Member

    Messages:
    4
    Location:
    Pittsburgh, PA
    Good Morning!

    I have a Bryant model BW2AAN boiler that was installed in 1999.

    Last week I was trying to bleed the upstairs radiators but was unable to get any air or water out of te bleeders. I manually cycled the water valve to introduce more water into the system (the gauge read just under 20 psi) and I was able to bleed the radiators.

    Today I was checking the water pressure and it was up to 30 psi. I drained the boiler down to reduce the pressure to 17 psi but am wondering why this situation occured.

    I have one of the old expansion tanks suspeneded in the rafters in the basement. If this becomes filled with too much water would that hinder the system's ability to properly regulate the water pressure? Would isolating it and draining it down allow my system to rebalance?

    Thanks in advance for any and all information.

    Thanks!

    Jeff
    Last edited: Feb 8, 2011
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,143
    Location:
    New England
    Three things:
    - the expansion tank could be shot. It should be mostly full of air. If it sounds like it is full of water, it's probably shot.
    - the autofill valve (if you have one) is leaking, and needs to be replaced
    - the manual fill valve (if you don't have an autofill valve) is leaking, and needs to be replaced
    - and maybe a fourth - if you have an indirect WH or a hot water coil, it could be leaking internally, and the potable water system is pressurizing the boiler circuit.
  3. jgraves

    jgraves New Member

    Messages:
    4
    Location:
    Pittsburgh, PA
    I just got home and checked the pressure - it was back up to 30 psi.

    I drained the expansion tank - which is one of the old style tanks suspended from the floor joists - and only got about a quart of water out of it. I drained enough water out of the boiler to lower the psi back to 18.

    I was going to shut off the valve after the auto fill valve to see if that stopped it.

    I'm not sure exactly what you mean about number 4, but my hot water heater and boiler are separate systems.

    Any additional thoughts?
  4. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,143
    Location:
    New England
    If you have a stand-alone WH, then it doesn't have a coil in it that could be leaking, adding water, and therefore pressure, so that's probably out!

    That style of tank has it's good and bad points. Because it has to have air in it, some can be absorbed into the water, and then needs to be purged out. Then, eventually, the tank gets full of water and there's no room for expansion. But, it doesn't have a bladder to fail.
  5. jgraves

    jgraves New Member

    Messages:
    4
    Location:
    Pittsburgh, PA
    Since there wasn't that much water in the expansion tank I'm going to assume that isn't the issue.

    I did turn off the feed valve and when I checked the pressure in the morning it was just over 20 psi.

    What should the "at rest" pressure of the boiler be?
    What should the pressure be when the boiler is operating?


    I'm at a loss as to what I should be looking at next.

    Thanks for all your help.

    Jeff
  6. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,143
    Location:
    New England
    The static pressure of a boiler depends on two things (That I know of): how hot you make the water and how high you need to pump it (change in elevation). 20-pounds is probably a fair value for your system, but you'd need to provide more info to be certain. Most boilers have a low-pressure cutout switch...it must be above that or the boiler won't fire (risks flashing into steam), and they also have a T&P valve that will open if the pressure or temp gets too high. On a boiler, that pressure could be as low as 30-pounds, or it could be higher, depending on the design and use. Think of that as sort of the radiator cap of your car. It sort of sounds like the autofill valve may be leaking. This could be that the stem had crud on it and when you opened it, it can no longer easily seat, but I'm sure there are other reasons it could leak as well. Not sure if there is a fix other than replacement. If you turn the shutoff to the autofeed back on, does the pressure gradually go up? Note also, that the autofeed may have an adjustment on it, and changing that may solve things.
  7. jgraves

    jgraves New Member

    Messages:
    4
    Location:
    Pittsburgh, PA
    Well I'm still having issues. A friend of mine came over to take a look and said the air bleeder on the boiler is shot and needs replaced. I had a failed attempt to replace and will give it another shot when the weather breaks. Things were looking good then the pressure rose again since last night.

    I took out a radiator in the upstairs bathroom during a remodel and have yet to replace it. I'm assuming that both the supply and return lines have air trapped in them that is messing stuff up as well. I was going to join them and install a bleeder but just ordered the radiator so we can do that swap at the same time.

    Can the old style expansion tank fail?

    Thanks again!

    Jeff
  8. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,143
    Location:
    New England
    An old style expansion tank has the water exposed to air, the circulating water will absorb some on the way. The air extraction (bleeder) is therefore more important than on some other systems. Because you need to then drain off the water, this means that you are regularly adding both air and fresh water to your system. The air is the enemy - water that's been in a closed system for awhile will have had all of the air purged. Adding air means adding oxygen and other gasses. This can change the pH and the oxygen can add to corrosion (rust) of any iron in the system. Keeping air out of a boiler system goes a long way towards improving the service life. You might look into something like a Spirovent and a properly sized bladder tank. If the spirovent does get clogged up, it can be taken apart, cleaned and put back into service.
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