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Slow loss of pressure - should I pursue repairs?

My 1880s 3-story house has a circulating hot water heating system, with cast iron radiators on all floors and a 20-year-old gas boiler in the basement. The system slowly loses pressure. I'm wondering if I should be concerned, whether I should pursue repairs soon (or safely defer until later), or whether I should simply keep adding water to the system.

We bought the house over the summer. When I tried to bleed the 3rd floor radiators a couple of months ago, the system had a vacuum at the top and pulled air in! I tracked a problem to the pressure reducing valve (Watts model 1156F); the valve was full of dirt & sludge, but once I cleaned it I could then add water to the system from the street.

I brought the system up to 15psi, bled the radiators - so far, so good. After the boiler turned on, the system pressure got up to ~20psi. A week or two later, I noticed that the pressure had dropped. There's a slow leak from the pressure relief valve, although it states that it's set to 30psi and the system pressure has not raised that high. I have not noticed any other leaks.

I have tracked the system pressure and the water volume leaking from the pressure relief valve over the past few weeks. I've added water via the fill valve (through my newly-cleaned pressure reducing valve), but I don't know exactly how much. Over one four-day period, the pressure dropped from 20psi to 8psi, and the pressure relief valve leaked about a half gallon. I opened the fill valve for ~30-45 seconds to increase pressure from ~8psi to ~15psi. Graph below.

Replacing the pressure relief valve seems like an obvious first step. Should I do so soon, or wait until spring? Is it likely that there's another leak elsewhere? What else should I consider?

Thank you in advance for the advice!



  • STEVEusaPA
    STEVEusaPA Member Posts: 6,505
    -Where's the expansion tank, and what kind?
    -Did you confirm pressure with a separate gauge, known to be good? You may think you're at 15 psi, but could be much higher.
    -Adding water adds air. The newly added air may be causing the relief to pop. Then adding more water adds more air, and over and over again.
    -If you have a steel expansion tank, it may be water logged. A bladder type tank may have failed.
    -Continuously adding water will kill your boiler.

    A competent hydronics pro should come out and look over your system, find the leak, if any, fix/repair any components, properly bleed/purge the entire system, and get your system back to normal.

    There was an error rendering this rich post.

  • reedshea
    reedshea Member Posts: 2
    Hi Steve,

    The expansion tank is an Amtrol Extrol EX-60, and is located above the boiler off of the supply pipe. It looks to be in good shape. The indicator cap suggests no problem, and tapping the tank it sounds mostly empty. It sounds like there is water in the upper 15% of the tank, above the bladder.

    I did not measure the pressure with a separate gauge. But the pressure reducing valve's factory setting is 15psi and shut off automatically (I can hear the water flow slow) at about that pressure on the gauge.

    Is there anything you'd suggest I try myself? Sounds like some professional help might be worthwhile. I'd prefer not to kill the boiler. :) (Although, I may pursue replacing it with a condensing boiler within a few years in order to be able to remove the chimney.)

  • Jolly Bodger
    Jolly Bodger Member Posts: 209
    Now is your chance to check out a Pro before buying a whole new system.
    If tapping on the tank proves it is in good shape and properly charged, then just get out your witching sticks to find the leak. ;) (all in good fun)
    Tanks, valves, seats, gauges, and settings all wear out. That is why we carry tools and test instruments and test.
  • Jamie Hall
    Jamie Hall Member Posts: 23,446
    And while you are poking around to find leak or leaks, remember that even a very small leak can cause what you are seeing.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England