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pressure problems

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Jim_4
Jim_4 Member Posts: 6
in THE MAIN WALL
Customer has an old boiler that runs at 35 lbs pressure and leaks a small steady stream from the pressure relief valve.
We know it is not a pressure reducing valve problem, because we shut off the water supply and it the pressure stayed the same. We can not find an expansion tank either in the basement or the attic or any upstairs closets.
The 2nd floor has 3 old cast iron radiators, the main floor has baseboard heat, and the basement has a separate circulator with an old radiator. The boiler also has a circulator for the 1st and 2nd floor. We are not sure of the cause of the excess pressure or how to correct it.
Would appreciate any help.

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  • Joe_5
    Joe_5 Member Posts: 19
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    old gravity system?

    Jim, sounds like you may have an old gravity system. Big 2'-3' pipes in the basement? If so, we ran into a job just like yours last May. Expansion problems caused by no expansion tank. One of my techs adv the customer that the boiler's relief valve couldn't be piped directly into the sewer. After we corrected it, we couldn't control the water pressure. Long story short, the system was designed using radiators that were meant to have their upper 1/3 filled with air. Each rad was it's own little exp tank. This system still didn't have pumps, and didn't need them either. The guys here on The Wall helped us greatly to correct this mystery job. We used a chart in Dan's book, How Come?, and sized 2 #60 Extrols. We also set the fill and tank pressure to 15# to maintain at least 1-2# in the 3rd fl rad. The job is running like a charm. This help? Joe
  • Mark J Strawcutter
    Mark J Strawcutter Member Posts: 625
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    distributed expansion tank

    Perhaps it's one of those systems where they used the top of each radiator as an expansion tank?

    If the first floor was originally CI rad and later replaced with baseboard that would have reduced the expansion area available.

    Then if someone bled all the air cushion out of the upstairs radiators - no expansion tank(s) and resultant pressure problem.

    Just a thought - either that or they were _really_ creative about hiding that tank!

    Mark
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