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Premature auto water shut off

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Steam heat here and the sight glass is somewhere around 2/3 full, or at the recommended level. But sometime during a heating cycle the McDonnel auto water shut off kicks in and turns off the furnace (little red light turns on). About 30 seconds the red light turns off and the furnace turns back on. I can't imagine this is good for the furnace, there's definitely water in the sight glass, and it hasn't done this previous winters. It doesn't appear this water shut off has a blow-down nor does the sight glass appear to have a sensor in it. I can't figure out the exact model but it appears to be an earlier version of McDonnell & Miller PS-800 whose description says it doesn't need to be blown down? Can anyone make recommendations, or has experienced this? Thank you!

Comments

  • Fred
    Fred Member Posts: 8,542
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    Post some pictures so we can see the boiler, piping and especially the Low Water Cut-Off (LWCO). Does the water level in the sight glass bounce a lot when the boiler is running? More than 1/2 to 3/4 of an inch? Have you have any piping work done that might have put some oils in the water since the last time the boiler was skimmed? It is possible that the boiler needs to be skimmed. If there is a lot of bounce, that is an indication that skimming is necessary as that bounce may make the LWCO think the boiler is low on water. Also, depending on how and where your LWCO is mounted, there is a probe somewhere but it is not in the sight glass. It is probably in a boiler tapping, maybe even behind the unit itself if it is mounted directly onto the boiler. That probe may need cleaning or be faulty but I suspect you have a lot of water bounce since the LWCO does reset itself quickly after shutdown.
    Gryfon19
  • kcopp
    kcopp Member Posts: 4,448
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    When was the last time the probe was pulled and cleaned?
  • Gryfon19
    Gryfon19 Member Posts: 20
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    We have in fact had work done where oils would have gotten in; however, the system was flushed and the boiler/sight glass re-filled only about a week ago (post-work). I'm familiar with the water bounce, but now I'm seeing, at times, the water in the sight glass drops almost to the bottom when it's running. And then strangely enough, after it's finished and settled the sight glass may be completely full. All this after it was first set to about 2/3 full.

    Sounds like skimming is likely the solution. As I've read about it, I'm not sure it's something I'm comfortable doing myself so I guess it's time to call the plumber.

    The insulation was also removed during the work, which I suspect is causing many of the radiators to hiss, presumably because some amount of the steam is quickly changing back to water and passing through the vents as fairly wet steam. I know, I need to pick up some insulation and install it. I looked at Lowe's online but I see they carry only half inch size and it seems I should use at least 1 inch.
  • Waterbury Steam
    Waterbury Steam Member Posts: 58
    edited November 2014
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    The immediate solution if it's surging that much will be skimming. Unfortunately, the near boiler piping looks pretty jacked up and will likely be surging and sending really wet steam into your system no matter how clean the water is. Does your system hammer while it's running?
  • Gryfon19
    Gryfon19 Member Posts: 20
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    We get a little hammering from time to time what about the piping is "jacked up" and would cause wet steam?
  • Gryfon19
    Gryfon19 Member Posts: 20
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    Is it possible that if either end of the sight glass were closed (or nearly closed) that would cause the water dropoff when the boiler is on and cause the LWCO to shut off periodically only to turn back on 60 seconds later?
  • David Nadle
    David Nadle Member Posts: 624
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    The bottom leg of the sightglass may be clogged and the actual water line is lower than you think.
  • KC_Jones
    KC_Jones Member Posts: 5,749
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    The bottom leg of the sightglass may be clogged and the actual water line is lower than you think.

    Good point. Have the sight glass valves been flushed out and cleaned? Did they add any chemicals when they did the flush? If they did and raised the PH too much it could be foaming which can make the sight glass and water level go crazy as well.
    2014 Weil Mclain EG-40
    EcoSteam ES-20 Advanced Boiler Control
    Boiler pictures updated 2/21/15
  • Gryfon19
    Gryfon19 Member Posts: 20
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    What I saw if that the sight glass goes from the appropriate water level to virtually empty when the system runs. After it turned off, the sight glass would eventually fill full.

    Last night is emptied the boiler. The sight glass was still full but the LWCO light came on. Strange because it seemed full. I can't be sure but I'm wondering if the plumber, after doing a lot of work, inadvertently left either sight glass valve closed as so what I was seeing for a water level wasn't accurate.

    This morning I made sure both sight glass valves were open and water level at the appropriate level. I checked periodically while the heat was running and the water didn't seem to bounce at all and the heat never (I think) shut off due to the LWCO.

    I want yo embrace the steam heat but it's always something, and keeps me up at night (figuratively and literally).
  • nicholas bonham-carter
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    If you can hear the radiator vents, then that is an indication that the main vents are inadequate, and that the pressure may be getting too high. High pressure will temporarily force water out of the boiler into the returns. The water comes back when the burner cuts off.--NBC
  • Gryfon19
    Gryfon19 Member Posts: 20
    edited November 2014
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    When you say main vents, do you mean the vent on the steam pipe in the basement that leads up to the rest of the house? If so, how are they rated? It looks like the plumber replaced the vent on wha I believe is the main pipe, so maybe the opening in the vent isn't large enough? Is there a method for gauging the appropriate size of the vent for the main pipe?

    I should also mention the pipes aren't insulated, so I was previously assuming that was causing steam to convert back into water and essentially passing a wet steam through the radiators and out the radiator vents = hisssss.
  • Fred
    Fred Member Posts: 8,542
    edited November 2014
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    Just flushing and refilling the boiler won't get rid of the oils. They just cling to the sides of the boiler cavity and when you refill it, they are right on the surface again. Both the upper and lower valves on the sight glass should always be fully open except when you are doing maintenance on the sight glass. I hate to say it but like others have said, the near boiler piping is really bad. It should be black iron threaded pipe. Copper will eventually break at the solder joints from all the expansion/shrinkage. The riser comming up out of the boiler should go into a header that is at least one size larger pipe diameter. The main should come off of the header and the equalizer should come off of the end of the header. The Hartford loop does look high but it should also be tied in with a "close" nipple. The way it is set up now, it must be causing some banging. I am sure you have wet steam but it is from the piping set up, not the lack of insulation. If I were you, I wouldn't spend any time or money on insulation until the piping is fixed. Put more vents on the main and make sure the Pressuretrol is set at .5psi cut-in and a differential of 1psi and make sure the pigtail the Pressuretrol is mounted on is not plugged with gunk. Those things are probably the cause of the Hissing radiator vents. If you stay with it and get the system problems fixed, you will love steam. It can be frustrating trying to correct problems you may have inherited but that is true with anything. The key is to get things fixed and not live with known problems and stress over when the next issue will bite you in the "A..". If you have the owners manual for that boiler, read over it and note the recommended piping installation and if you have a contractor make the corrections, make sure he understands that is how you want the job done.