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relation between temp rise and preasure rise

I just finished installing a WM GTO3 following the pumping away suggestions and diagrams in Dan's book. 3 zones, one story ranch. It was a retrofit replacing an old New Yorker steel boiler. Filled the system cold to 12 psi with a new Extrol #30. After firing the system, the preasure rose and I removed enough water to keep the system at 13 psi at 150 deg. How much of a preasue rise should the system see when the boiler reaches it's high limit of 190 deg. I'm reading preasuer at the guage directly on the boiler. I'm getting about a 5 deg rise/change in preasure as the water expands.


  • Al Letellier_9
    Al Letellier_9 Member Posts: 929

    You will get the most expansion when you fire up a cold boiler for the first time. Once you get up to temp and trim the pressure, it should stay relatively stable. With the TGO boiler you have a coil and the boiler will stay up on limit all the time. The rate of expansion is less at that level as the temperature swing is less ( 20 degrees).
    If you continue to see swing in pressure, make sure the xtank is properly charged. Just 'cause its new doesn't mean its charged correctly. With the system pressure off the tank, it should be charged with air to the normal operating pressure of the system ( 15# is about right).

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  • Timco
    Timco Member Posts: 3,039

    Your new system will give off gasses from the fresh water, and need to be bled and refilled for a week or so, until you maintain pressure and have no air. Only fill cold.

    Just a guy running some pipes.
  • Our simple method

    is to have the boiler and all the zones bled of air , and the boiler cold . Let it heat to it's high limit and see where the pressure is at . We aim for under 20 psi . Anything higher and we'll throw on a 2nd tank . But a 30 Extrol is usually plenty good for typical residential homes with hot water heat other than cast iron rads or gravity systems .
  • hr
    hr Member Posts: 6,106
    You need to size the tank correctly

    also. For an accurate expansion tank sizing you need the system volume, temperature from start up to setpoint, fill pressure, highest point above boiler and desired pressure at that point, and the fluid in the system.

    Contact a dealer or rep for help sizing the tank. The HDS program also has a simple easy to use expansion tank sizer.

    Never hurts to oversize. And ALWAYS check the precharge on bladder tanks. Hardly ever find one at 12 psi, as indicated :)

    hot rod

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  • mark schofield
    mark schofield Member Posts: 150

    thanks for the replies
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