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high pressure

We are currently renovating a 1920's house with a one-pipe steam system. The boiler is not very old (maybe 10 years). We have not been using the heat much yet this season so far but turned it on this morning for a while. It had been running for a little while when I noticed that the windows near the basement were a bit fogged. It turned out that the pressure relief valve (blow-down valve?) was blasting away and the basement was full of water vapor. I immediately checked the pressure gauge which was reading up around 10psi. All last winter it was consistently operating between 2-3psi.

Special circumstances:

We have several radiators (actually nearly all) pulled & lines capped in rooms where we're doing renovation work on the 1st floor. Could this condition cause the boiler pressure to shoot up like that? I assumed that the system pressure would be unaffected.

Does this mean that the system has a faulty pressure regulator? And could the boiler have been damaged by running at that high pressure when the system usually operates much lower?

Thanks in advance for your input.


  • Jamie Hall
    Jamie Hall Member Posts: 19,966
    If the pressure relief valve

    is blasting away, do yourself a favour and turn off the system at the emergency switch and leave it off until you find out why.  That valve is your last defence against catastrophe, and the fact that it's opening indicates that the pressuretrol (or vapourstat) on your boiler is not operating.  It is supposed to turn off the burner at some low but reasonable operating pressure, which should be less than 2 psi.

    Possible problems, not an inclusive list: the pressuretrol is bad.  The pigtail to the pressuretrol is clogged.  There is a short somewhere which is taking the pressuretrol out of the circuit.  And so on.

    It is unlikely that the boiler was damaged, unless it ran dry (while you're at it, and after you get the pressure problem fixed, do check the low water cutoff!).  However, equally it is likely that any vents on the system have been damaged; while some vents can take up to 10 psi -- and some even more -- most aren't rated for more than that.  Ditto thermostatic traps.  So you may have some problems when you get started up again.

    But: Turn That Thing Off and get it fixed!
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • mtb500
    mtb500 Member Posts: 4
    it's off alright

    believe me...the first thing I did was hit the kill switch.

    thanks for the reply...I will check all of that stuff out.
  • mtb500
    mtb500 Member Posts: 4
    Do you think having

    a bunch of radiators temporarily off-line be causing any related problems? The pipes have been banging around more than usual and I have chalked it up to the system being grossly unbalanced as a result of the closed lines.
  • Steam Heating

    As Jamie stated your problems is with your boiler controls, most probably the centered around the Pressuretrol or vaporstat which ever is installed. The closed off radaitors would only make the boiler shut off sooner as the system wouldn't require as much steam.

    There are some very good books offered on this website on steam heating. I keep pitching them as they were such a big help to me. The first one i would get is :"We Got Steam Heat"  It written for the homeowner, humorous, and in a few evenings you'll know more about steam heating than most people.  Here's a link to the book.


    The second one I would get is "The Lost Art of Steam Heating". This goes into steam heating systems in more detail. If you consider getting both books I would go with the "Steamy Deal"


    as it includes another book on troubleshooting steam problems.  Steam Heating is actually very simple but you must follow certain basic rules and since you're moving things about I thought these books might be beneficial to you. For me, these books have paid for themselves a hundred times over. One of the big benefits from reading these books is that you get enough knowledge to know whether the 'heating professional" you are talking to knows anything about steam and you'd be surprised that a lot unfortunately don't.

    - Rod
  • mtb500
    mtb500 Member Posts: 4
    You are absolutely right

    about getting enough knowledge to spot a contractor (in any trade) that is inexperienced. After doing renovation work for the last 15+ years or so, I've found it easier & easier to notice that the "pro" I'm talking to doesn't necessarily know what they're doing...and vice versa...enjoying the comfort level of talking to a real professional that obviously knows their stuff inside & out.

    Thanks for the book references...
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