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Pressure needed to burst cast iron baseboard

This past March I was called to find and fix a leak in a section of cast iron base board on a single zone hot water system. What I found was a split in one of the sections, not a faulty push nipple as I had suspected.  In my eyes it was clearly a freeze split.  Knowing this customer I am pretty certain the freeze occurred long before he and his family moved into this single floor house.  I replaced the run of base board thinking it was odd that it held for so long and that this is an anomaly...  Well a month ago another section went.  Clearly in my eyes another freeze that held on for god knows how many years. 

Home owner wants to know if the boiler could have over pressurize and split the cast.  I said no that the relief valve and an assortment of other things would have opened before the castings would.  He doesn't believe me and has run a number of scenarios by me.  So Can any one tell me the pressure rating of Crane cast iron base board?  And can anyone tell me the pressure rating of a simple coin vent?

Thanks for any help here.




  • Big Ed_4
    Big Ed_4 Member Posts: 2,700

    Well ,you should have a boiler relief valve that releases at 30# , and the norm would be the radiators are higher then the relief so it would experience a lower pressure ... Not sure the rating but sure rated higher then 30#... You have to remember those crane radiators have been around years longer then you have...My questions are , what has changed ? And how long ago did they buy the house ... Any change in the supply piping for a thermal shock ? Or maybe someone did a quick fix with boiler sealer in the past?? My feelings... boiler sealer which is a temp fix ....
    I have enough experience to know , that I dont know it all
  • bob_46
    bob_46 Member Posts: 813
    Max Pres

    Burnham Baseray is 30# max water, 15# steam. I agree with Ed

    it probably froze at sometime and was fixed with stop-leak.
  • Rod
    Rod Posts: 2,067
    Coin Vents

    Coin vents - Most I've seen are about 125PSI. I'm assuming you need some printed info to back yourself up so here are some links and attachments to info and specs.


    Look down the Taco sheet. There is a table of specifications farther down.

    I concur with the freezing /sealing. scenario.

    - Rod
  • meplumber
    meplumber Member Posts: 678
    Ran in to this myself.

    I ran in to a similar scenario a few years back.  It was a case of a freeze up that caused some hairline cracks in the cast iron baseboard.  The heat guy "fixed it" with Stop-Leak.  It held for a while and then started letting go a piece at a time.  By the time I was done, I had replaced almost half the baseboard in the house.  The homeowner didn't believe me at first either.  Luckily I happened to run into the old plumber at the supply house one day and asked him.

    We live and learn.
  • Matthew Grallert
    Matthew Grallert Member Posts: 109
    freeze up

    I agree that this was a freeze up at some point.  The pieces went one at a time (three sections)  I have removed all of it now as the HO and his wife have lost faith in it after the last and worst opening, can't say I blame them.  The strangish this is they have lived in this house for more then thirty years.  House was build after the second world war and well built at that.

    This is just the kind of info I was looking for, thank you so much.


  • kev
    kev Member Posts: 100
    split baseboard

    Cast iron would not expand and split like a piece of copper. It cracks for good. I had a similar job where a leak developed in the cast baseboard and it also looked at first like a crack and then on further inspection more like a bad cast. This baseboard was over 30 years old. Assured the customer this was a rare thing and to not worry. Sure enough a month later the same thing showed up on a section in another part of the house. That was over a year ago. I checked every place for a leak thinking the system at one time was taking on fresh water and causing corrosion. Everything was original no leaks. Fingers crossed.
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