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Steam vents not reopening

Apologize if this should have been simple to find by search but I couldn't find it...

Just this year I've started to have a problem on multiple radiators where a tenant complains that their room is cold. Historically I always check/replace the vent as a first troubleshooting step. Most frequently when I remove the vent, a few drops of water come out of the vent, and, assuming the system is running at the time, I can feel air flowing out of the vent hole and the radiator starts warming up, section by section, as it should.

If I blow back into the exhaust hole on the vent, I get another bit of water out (less than an ounce probably), and then I test to make sure the mechanism isn't stuck by blowing in to the inlet with the vent hole facing up, then down, then up again (confirming that the mechanism moves and stops my air flow when the vent hole faces down.) After reinstalling the vent, the radiator works fine for several days or weeks before I get the "my room is cold again" call. In previous years at that point I've just replaced the vent and the problem has gone away for the rest of the year. However this year in at least two cases, the replacement vents continue to do the same thing.

It seems to me as if the vents are trapping condensate inside the vent, effectively keeping the vent closed. A quick blow throw the vent hole to purge the water solves it... for a few days.

Thoughts? Is it just cheap vents (maid-o-mist, now durst, available at my local box store) or is there something else going on?

Comments

  • JUGHNE
    JUGHNE Member Posts: 11,021
    What pressure does the system run at?
  • neilc
    neilc Member Posts: 2,663
    and are the rad valves fully open ?
    known to beat dead horses
  • Fred
    Fred Member Posts: 8,542
    And are the radiators pitched back towards the supply valve?
    When was the last time you cleaned the pigtail that the Pressuretrol is mounted on? If it is clogged, the Pressuretrol can't see the pressure and shut the boiler down before it builds well past what it should be. In that case, the pressure may not be letting the water out of the radiator and may well be blowing it back into the vent.
  • dev_hollows
    dev_hollows Member Posts: 18
    Cut in is set at 0.5 with a diff of 1. Radiator valves are fully open. Radiators are pitched back.

    However, I have never cleaned that pigtail. Totally possible it’s not operating properly. I suppose that means on cold days if it builds up too much pressure, the thermostat will call for heat again before the whole system cools down enough to relieve the pressure?
  • Fred
    Fred Member Posts: 8,542

    Cut in is set at 0.5 with a diff of 1. Radiator valves are fully open. Radiators are pitched back.



    However, I have never cleaned that pigtail. Totally possible it’s not operating properly. I suppose that means on cold days if it builds up too much pressure, the thermostat will call for heat again before the whole system cools down enough to relieve the pressure?

    Probably not but certainly the boiler will run past an acceptable pressure during a call for heat and, if there is enough pressure, it could prevent water from getting out of the radiator and possibly blow some up into the vents. Also, anything much over about 3PSI can ruin the radiator vents.
  • dev_hollows
    dev_hollows Member Posts: 18
    Guess it’s time for a working pressure gauge and a pigtail cleaning...
    JUGHNE