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hot water gas boiler problems

salio Member Posts: 18
I have a 20 yr old Weil McLain cgi gas boiler, 133,000 output. It's a converted gravity system with 524 sq. ft. radiation and 4" (I think) main supply and return lines, with the circulator on the return line and a separate Lochinvar water heater. The system was designed by Fremont Lobestall for those who knew him.
For several years the boiler has relieved out of the pressure relief valve


  • neilc
    neilc Member Posts: 2,087
    isolate and drain the compression tank,
    post some pictures
    known to beat dead horses
  • neilc
    neilc Member Posts: 2,087
    what do you see for pressure?
    12 ~ 15 ?
    still, isolate and drain the compression tank,
    feeder valve leaking by? isolate it too,
    and you probably need to replace that relief valve too.
    known to beat dead horses
  • salio
    salio Member Posts: 18
    Sorry, computer was acting up and somehow posted the question before finishing, here's the rest of the story:

    Boiler pressure was running around 20 lb. Spoke to a mechanic who told me how to adjust the pressure reducing valve and had mixed results with that. Last year the boiler sections began leaking. I ended up tearing the whole thing apart - 5 cast iron sections. The seals all looked good to me and they wanted something ridiculous like $300 for 8 new seals. So I flushed everything out, cleaned all the mating surfaces, applied permatex over the seals and around the perimeter, installed a new, larger expansion tank, new stainless steel burner tubes, new power vent fan, and reassembled everything.
    It ran great - for a while. Then the boiler would run, but constantly cycle on/off, with 1-2 seconds running before cutting out. Had the mechanic over again, and found that my new fan housing had a port for one of the vacuum lines, so we connected the line to that port, and plugged the port on the draft hood. This time the boiler fired and ran until the thermostat was satisfied. Now, the boiler has started leaking again, so this time I installed Hercules Boiler Liquid, 2 quarts, and that stopped the leak - for a while, and it was firing fine. But now the pressure reads 20 lbs again - with the new expansion tank. And now it's cycling again on/off again, running for 1-2 seconds before shutting off and coming on again. At 15 deg F outside temp it can keep the house warm, but with -15 coming in a few days, it won't. That's pretty much it. The mechanic had earlier suspected the vacuum switch, but when we moved the hose to the power vent housing, it had worked for a week or so. Now I'm wondering about that switch again, and still have this excessive pressure. As long as it's cold enough outside to require regular firing, the boiler stays hot enough and doesn't leak. But on a warmer day when the boiler cools off, it will start leaking again.

  • Intplm.
    Intplm. Member Posts: 1,417
    Did you use the boiler liquid before you did that major repair or is this the first time.
    Boiler liquid can plug holes that you need and not just leaks. This could be one of the causes of your short cycling?
  • salio
    salio Member Posts: 18
    I used the boiler liquid only recently after the major repair. It was short cycling before that, and oh, replaced the pressure relief valve with the rebuild as well.
  • neilc
    neilc Member Posts: 2,087
    pressure will rise some when the water heats,
    or is the cold fill up at 20 also?
    Is domestic connected, maybe that's leaking in?
    or the fill valve leaking by?

    As for the cycling, and the pressure switch,
    ports clear? hose secure? switch good? wires tight?

    you need a tech there
    known to beat dead horses
  • salio
    salio Member Posts: 18
    Haven't checked the cold fill pressure recently - it's running all the time right now. Separate domestic hot water heater, but I have wondered about the fill valve. Don't know if the pressure switch is good or not. You're right, I need a good tech. Some of the guys they send don't seem like experts to me, this is why though I'm a carpenter I've taken it upon myself to get more involved. And while I respect the trades, the high rates in this area are a bit hard to swallow. If I knew I could get an expert in it would solve a lot of problems!
  • salio
    salio Member Posts: 18
    Ok, we made it through the worst of the cold weather, thankfully. I think the boiler was running almost non-stop, and this kept it hot and swelled tight so it wouldn't leak. Maybe it's not the pressure switch after all.
    Now that it's warming up a bit and the boiler is cycling off and cooling down, it has started leaking again and wouldn't fire by afternoon. This is what I did (remember, I'm a carpenter not a boiler mechanic):

    1) Lowered the boiler pressure via the pressure reducing valve and opened the relief valve to get down to about 10 lbs. pressure (cold).

    2) Tightened the three rods (again) that hold the sections together, about as tight as a 200lb man can get them with an end wrench (no pipe or breaker bar yet) - don't want to snap off the cast iron tabs - is that a possibility? Doesn't seem like they should have to be tightened that much, is there a torque value?

    3) Removed the (stainless steel) burner tubes, cleaned them out good with a wire wheel and dried them out

    4) Igniter was also wet from the dripping boiler, so I lit some paper, held it in there, and it lit, but would cycle off before all the burners could light. I kept repeating the cycle until finally something got hot enough and all the burners lit. House temp was down to 60, so it'll run for a few hrs before it reaches 70 (remember, converted gravity system w/ 4" main lines).

    Here's are some of my questions:

    1) What's up with the seals on these W-M cgi boilers and why is this thing leaking when it cools down? It's not expanded from the heat, I know, but why is it leaking? The seals all looked to be in good condition when I took everything apart last year (read the original post), so I re-used them and applied permatex high temp gasket sealer on top of each one, in place of the sealant they supply with new (ridiculously overpriced) gaskets. This worked for about a year, but somehow my boiler pressure increases to about 20lb and it somehow started leaking again this year. Last year I also installed a new 30lb expansion tank (original one was 15 lb), and it doesn't sound like it has any water in it at all.

    2) So do I take the sections apart and rebuild it again but this time spend the money on new seals? Can I get the seals from some other supplier to reduce the cost? Do I just stop everything and try to find an experienced boiler mechanic?

    Thank you ahead of time. If I should tear it apart and re-seal the boiler sections, this weekend would be the time to do it, assuming I can get the seals in a day.

  • Gordy
    Gordy Member Posts: 9,537
    When you set the pressure for the new expansion tank did you do it isolated from the system?

    If so, and system pressure was set, did you shut the supply valve to the water feeder off to be sure that it is not the culprit letting water into the system?

    The seals may have been leaking when the boiler was running hard. The water was probably flashing to steam, and going up the flue before it hit the floor so you didn’t notice.

  • Jamie Hall
    Jamie Hall Member Posts: 20,466
    On those seals... and the tie rod tension. The seals are -- at least on the bigger WMs -- a square section O-ring. They should seal with good torque (do it evenly, like you would a cylinder head) but not excessive torque. Permatex won't hurt them -- may not help much either. The problem is that like most O-rings they take a set once they are installed. As a general rule, even if an O-ring looks good, it should not be reused. I don't know if there are "just as good as" O-rings available for WMs -- but if it were mine I'd use OEM rings.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • salio
    salio Member Posts: 18
    The expansion tank pressure was set from the factory. There 's a shut off valve just upstream from the tank and that was shut before the tank was installed, and actually the boiler and near piping were drained at that point.
    On the O-rings, yes, mine are a square section as well. It was a complete rebuild of the boiler last year so just taking the heat exchanger out and rebuilding that won't be so bad. Maybe those seals did take a set from the previous 20 years and never made a good seal. Do those sections ever warp or get hairline cracks? I didn't see anything like warp last year; they all fit together very evenly. And I would think a crack would become pretty visible over time.
    Also, I still don't understand why it was short cycling for several months previously. It's not doing that anymore. The only thing possibly related is, we have an older well system and the tank does not have a bladder. Over time it looses air and I have to drain the tank, recharge with air to 28 psi, then turn the well back on and let tank pressure rise to 55-60 lb, at which point the pressure switch shuts it off. We did that during this same time period and the boiler was spitting and sputtering out the pressure relief valve. But after that episode I had no more short cycling?!? Now I'm wondering if that pressure relief valve could be faulty? But since then I made the adjustment on that valve it seems to be been holding -- it was at or below 10 lbs cold, and right now with the boiler running it's at 17 psi, and 185 deg.
    One last thing, is there another source for OEM seals without paying $300 for a set of 8 seals? That's just crazy.