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Spill switch tripping, water dripping at vent pipe seam, steam, humid

JohnRL Member Posts: 6
I have a Weil Mclain gas boiler, a little over 18 years old.

The spill switch trips 15 minutes to a half hour after starts up. There's water dripping at one of the seams in the vent pipe that goes from the draft hood to the chimney. Last night, after it had been running for awhile, I notice steam coming out of the vent hood of the water heater. The basement has been feeling warmer and humid lately too.

I attached a picture so you can see the configuration. I put a piece of foil over the damper motor because the water was dripping on it.

What might the problem be?



  • Jamie Hall
    Jamie Hall Member Posts: 17,039
    Check that chimney, sooner rather than later. Something may be blocking, or partially blocking the draught. It may be as simple as ice having formed in the chimney (yeah, it can happen) or something more drastic.

    Have there been any changes in the operating temperatures of the boiler?
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • JohnRL
    JohnRL Member Posts: 6
    No changes in the temperature as far as I know.

    I had a feeling it might be a chimney blockage. I was hoping I was wrong.
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,837
    I do hope you have carbon monoxide detector alarms throughout your home. This is SERIOUS, and as noted, needs IMMEDIATE attention, if not sooner...

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • JohnRL
    JohnRL Member Posts: 6
    I'm trying to get someone here now
  • unclejohn
    unclejohn Member Posts: 1,749
    Does it trip when the burner is running or after shuts down. in the picture the damper is shut.
  • JohnRL
    JohnRL Member Posts: 6
    It trips while it's running. It was off in the picture
  • ChrisJ
    ChrisJ Member Posts: 11,969
    Please let us know what they find.

    There's of course the opposite possibly, that the boiler and drafthood can't get enough makeup air from the outside. Same result, different cause.

    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
    Mark Eatherton
  • Gordy
    Gordy Member Posts: 9,514
    Just so you understand the higher level of heat, and humidity is the flue gases dumping into your basement. You need to shut the boiler down until this is resolved!
  • JohnRL
    JohnRL Member Posts: 6
    Yeah, I figured that about the heat and humidity. I have a chimney guy coming at 8:00 tomorrow morning. Tonight we're making do with a couple of space heaters
    JUGHNE Member Posts: 8,931
    Remember that the water heater is just as much of a CO threat as the boiler!! obviously have a partially plugged chimney which it shares.
  • Jason_13
    Jason_13 Member Posts: 299
    Could be a cold chimney. Saw a case like this that the chimney came through roof down by the spouting. When hot really cold could not draft properly.
    I also agree with the. Combustion air problem. Can you open a basement window and see if problem goes away. One cycle should determine this.
  • Gordy
    Gordy Member Posts: 9,514
    If it worked before, and does not now there is issues. Most likely in the flue.
  • JohnRL
    JohnRL Member Posts: 6
    It's cleared. There was a frozen nest of some kind in the flue.

    Thanks for the help everyone.
  • Gordy
    Gordy Member Posts: 9,514
    Get a chimney cap installed.