Boiler Pressure & T&P Relief Valve

Discussion in 'Boiler Forum' started by Gary in NJ, Sep 19, 2011.

  1. tray

    tray In the Trades

    Dec 9, 2011
    HVAC tech
    west henrietta, ny
    well for one in Rochester, NY that's what is sold and second i have seen bad pressure reducing valves at the house with water pressure nearly 150psi. In that case the valve need to be replaced and water authority brought in, talk bout a real long cold day. So id rather be on the high side for worst case scenarios
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Sep 2, 2004
    Retired Systems engineer for defense industry.
    New England
    I could see possibly on the main water supply, but not on a boiler. Boilers for most residential situations run less than 20#, and the relief valve is often in the 30# range, so one with a scale up to 200# is very hard to read in the normal working range with any accuracy.
  3. Tom Sawyer

    Tom Sawyer In the Trades

    Nov 29, 2010
    You put more than 30 lbs on the boiler and the relief valve is blowing off. There is absolutely no need for any other pressure gauge than the one installed on the boiler. If it's bad, change it. Jeeze talk about overkill.

    With any boiler system there are only a few things that will cause excess pressure.

    1 - bad or waterlogged expansion tank
    2 - High limit set over 220 degrees
    3 - bad or improperly adjusted auto fill (though it should be shut off after the boiler is pressurized)
    4 - A leak in the domestic hot water coil if the boiler is equipped with one.

    There are no other causes possible. Be sure you gauge is accurate before troubleshooting anything else and it can be checked by simply closing off all water feed sources to the boiler and draining the pressure off. The gauge should go to zero. Close the drain and open the feed. The pressure should rise to between 15 and 18 lbs and stay there.
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