New Boiler pressure at 24 psi???

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by philtrap, Sep 19, 2013.

  1. philtrap

    philtrap Member

    Messages:
    74
    Location:
    Long Island, NY
    Folks,

    I have a new installed boiler with a new cold water fill Pressure Relief Valve (PRV) which is factory preset at 12 psi. I also have a new expansion tank pre-charged at 12 psi, but the pressure in the system reaches 24 psi. I have reduced the pressure in the system to 12 psi and it always goes back to 24 psi. I've only run the boiler a few times up to 120 degrees and I'm pretty sure it would go up to 24 psi even if I didn't run it (i'm gonna try that over this weekend... not running it and seeing if the pressure raises).

    Any thoughts????

    The boiler directions say not to run it over 25 psi and the pressure relief blow-offs are 30psi.

    Thanks,
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,348
    Location:
    New England
    The autofill valve may be misadjusted, or it is leaking. Another possibility is if there is a leak in the heat exchanger of the indirect water heater, but it may go higher than the 25psi that you're seeing. Either the expansion tank is not sized properly or there's a valve between it and the rest of the system, is another possibility. Once you have your 12psi, shutoff the valve (hopefully, they installed one) feeding the autofill valve and see if it stays stable. If so, you've identified the autofill valve as the issue.
  3. philtrap

    philtrap Member

    Messages:
    74
    Location:
    Long Island, NY
    Thanks Jadnashua. I released the pressure from 24 psi to 12 psi by draining about 1 gallon of water from one of the lower heating loop valves. I shut off the water supply (and PRV) and ran the boiler for a while and the pressure raised to about 16 psi. The expansion tank is sized correct and the pressure from the tank is always the same as the gauge on the boiler. Do you think for this condensing boiler a rise or 4-5 PSI is normal or is there still a problem?
  4. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,348
    Location:
    New England
    The water pressure at the Schrader valve of the ET will ALWAYS be the same as your boiler's pressure if the gauges you use are accurate! The ONLY way to verify the WP at the ET is to relieve the water pressure on it, then check the air pressure, otherwise, as I said, it will always be the same at the boiler's reading. THey call it a precharge for a reason...it must have the proper air pressure in it before you insert it into the system, or you must relieve the water pressure on the bladder, then you can check the precharge.

    If the precharge is proper, and the tank is sized properly, the pressure won't normally vary more than a pound or so, if that, from my limited experience. If the precharge is too low, the bladder is stretched more than it is designed for, which can affect its longevity, and if it is almost non-existent, there's no room for the water to expand into, and the pressure will rise more as the temperature rises.
  5. philtrap

    philtrap Member

    Messages:
    74
    Location:
    Long Island, NY
    Thanks Jadnashua. The tank was precharged at 12 psi. I checked it before installing it. Maybe I'll take it off, check it again, release the pressure in the boiler and start over. The system is now at 16 psi. Do you think I should just see if it stays at 16 and live with it or is that too high? I can't see there would be a big difference, but I'm not sure.
  6. johnjh2o1

    johnjh2o1 Plumbing Contractor for 49 years

    Messages:
    1,143
    Location:
    South*East
    Even with a properly sized expansion tank there will be a slight pressure increase as the water is heated. 16 PSI is not going the hurt the system. But you do have a problem with the pressure reducing valve. It may not be adjusted correctly.

    John
    Last edited: Sep 22, 2013
  7. philtrap

    philtrap Member

    Messages:
    74
    Location:
    Long Island, NY
    Guys - I'm thinking it's the expansion tank. I installed a 30 gallon buffer tank in line with the boiler and kept the same sized expansion tank (but new) that was on the system before replacing the boiler.

    Here's the info:

    Heating system = 7.57 Gal
    Buffer = 30 Gallons
    Boiler = 3 Gallons
    TOTAL = 40.6 Gallons

    Min Temp = 80F
    MAx =180F
    Operating Pressure = 12 PSI
    Last edited: Sep 23, 2013
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