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All Radiators shooting steam, PSI normal... but can it be trusted?

Really frustrating situation here. All 9 of my radiators begin expelling steam at .5 psi and are simply screaming by the time the pressuretrol cuts out at 2.25.

Changed all radiator vents this season. Since doing so, all radiators began displaying the symptoms above.
changed the pigtail which was 100% clogged and refilled it with water.
Swapped the 30 psi gauge to a 0-3psi
changed the pressuretrol, replaced with same model.
Changed main vent from old 1/4" (likely clogged) and built a 3/4" riser with T at the top leading to TWO 3/4" main vents. The only main vent in the system is on the return, just above the equalizer and unfortunately right at the 90' - which is why I put a 6 inch riser on that.
Boiler fires and pressuretrol kicks off at 2 psi and kicks back on at .5 psi as expected which takes a full 50 minutes of firing to achieve.
However, the steam has all the radiators hot within 12-15 minutes from cold start - not bad at all! It then continues to fire until the pressure reaches .5psi (this takes about 40 minutes) At that time, all 9 radiators are pushing steam out of their vents. By the time the pressure reaches 1.5psi, each vent is shooting steam out so hard that the paint is being flicked off the radiators. Once it reaches this psi, all 9 radiator vents are rattling like baby toys. The pressuretrol kicks off at 2psi and the living conditions in the house are intolerable due to the insanely loud hissing.

I replaced all 9 radiator vents again. No luck, same symptoms.

Any thoughts??


  • Jamie Hall
    Jamie Hall Member Posts: 23,454
    Please see my reply on your duplicate thread.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • MikeBBudlong
    MikeBBudlong Member Posts: 8
    I created this in the wrong category by mistake. Can’t seem to delete it... loo