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LWCO trips during cycle

eclark Member Posts: 33
Was down in the basement cleaning a paint brush yesterday and noticed that my boiler cut out on low water during a cycle.  I've never seen it do that before, but it doesn't mean that it hasn't happened.  It tripped and was out for ~30 seconds while I presume water returned to the boiler.  For various reasons I have watched it run through full cycles before without issue. 


Burnham V8-5 (natural gas, circa 1991)

MM Probe type LWCO (new in November 2013)

It wasn't particularly cold when this happened (25 deg F maybe)

The boiler had been running for ~15 mins when it shut off.

Pressuretrol set for 2.25# cut out, 1# differential (per my 0-10psi gauge).

No previous issues with surge / bounce - just happy movement of ~.5" in the glass.

2" dia riser out of the boiler.  Main as a header (a problem I'm aware of but haven't acted to change this since we bought the house 3 years ago).

No main vents (need to tackle this issue this summer - I've been distracted with other issues in the house)

Any ideas for cause?  When I've heard of this happening before, it's been suggested to check for dirty water, clogged wet returns, overpressure, etc.  I kind of doubt it's clogged wet returns and I know I hope that's not the case.  Is there an easy way to check that though?


  • BobC
    BobC Member Posts: 5,408
    Slow return

    I assume you don't have an automatic water feeder on the boiler. Does the water level slowly drop an inch or more as the boiler makes steam? How long does it take the water to come back to it's normal water level after the boiler shuts down? What pressure is the boiler running at when making steam (just before it shuts down)?

    If the water level does decrease till it trips the LWCO it might indicate a slow return, do you have a valve on the return pipe so you can drain water out of it? If so open it up (when the boiler is just warm) and see if you get a lot of crud out of it.

    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • vaporvac
    vaporvac Member Posts: 1,520
    edited February 2014
    Which brand/model probe?

    I've recently read on this forum about some probes that shut off as a matter of course every twenty minutes and restart shortly thereafter. It's just how they're designed to work. Edit: this is the probe that does it: HydroLevel CycleGuard probe-type LWCO. The LWCO goes into "intermittent level test" (ILT) mode, shuts the burner off for a minute, and then restarts. CycleGuard models ending in 1090 do a 90 second ILT every 10 minutes, those ending in 2060 do a 60 second ILT every 20 minutes.

    If the other stuff doesn't seem to be the issue this may be the cause, since it's a new addition and you would have had to be there at the exact time to have observed it before. Just a thought.

    Another homeowner steam enthusiast... Colleen
    Two-pipe Trane vaporvacuum system; 1466 edr
    Twinned, staged Slantfin TR50s piped into 4" header with Riello G400 burners; 240K lead, 200K lag Btus. Controlled by Taco Relay and Honeywell RTH6580WF
  • eclark
    eclark Member Posts: 33
    No Auto Fill

    And I didn't get a chance to watch the glass for long enough last night but based on what I saw it takes 15 or 20 mins to get the water level back where it normally rests.  It did run through a full cycle without tripping the LWCO this time, but that just makes me think it is intermittent.

    I do drain a gallon or two off every month during heating season using the mud leg when it's warm (not hot) and i get lots of fine silty rust, but no gloopy stuff or big chunks.  Depending on conditions, the boiler is making anywhere between a few oz of steam and two pounds.  I forget exactly but i think I've got something like 180 sf EDR hooked connected via single pipe.

    V.V. - it's a mcdonnell miller ps-802-24.  No type of "automatic" testing that i'm aware of.
  • Flushing the wet return

    Do you have a separate valve for draining the wet return? On my boiler, I can valve off the boiler from the wet return, and as the water feed goes into the return, I can overfill the wet return, and then let that elevated waterline push any crud out the wet return drain.--NBC
  • eclark
    eclark Member Posts: 33
    I've got a drain valve at the boiler end of the wet return

    Just before the hartford loop.  And another drain valve where the hartford loop hits the boiler at the bottom of the equalize.  Are you referring to one of those?
  • vaporvac
    vaporvac Member Posts: 1,520

    Hi, NBC, I was just wondering if you have any pics of that set-up. Also, it was my understanding that the probe type LWCO negated blowing down the system regularly which helps prevent the introduction of too much fresh water. Should one still be blowing down the wet return regularly? Sorry to hijack your post, but it has raised a couple of issues I've been wondering about with my own install.
    Two-pipe Trane vaporvacuum system; 1466 edr
    Twinned, staged Slantfin TR50s piped into 4" header with Riello G400 burners; 240K lead, 200K lag Btus. Controlled by Taco Relay and Honeywell RTH6580WF
  • Flushing the returns

    My boiler has 2 drains at the back of the mud leg. These are connected by valves to the wet return. The water feed is connected also to the wet return. I can close the valves leading to the mud leg, and start the water feed, and fill the wet and dry return up to vent level. Opening the main drain in the other end of the wet return then washes out the wet return.--NBC
    RDSTEAM Member Posts: 134
    It's probably

    The new LWCO. some of the probe types have an intermittent level test every so often. Nothing to worry about.
  • eclark
    eclark Member Posts: 33
    I see what you mean

    My setup is a little different and maybe I misunderstood the term "mud leg."  Attached is a sketch of my configuration.

    I don't have any isolation valves anywhere in my piping so if i wanted to flood my wet return, it would flood the boiler too.  That seems like it might be a bad idea but maybe I'm being paranoid?
  • Piping problem?

    If your diagram is the exact layout you have, then I see no proper header/equalizer to separate out any water thrown up the boiler riser. That piping could just allow too much water up into the supply pipes. Then the excess water has a long trip to make all the way back to the return, during which time the boiler is starved (or made thirsty).

    If you look in the instructions, you will see the difference between what you have and what is required for correct operation.--NBC
  • eclark
    eclark Member Posts: 33
    The piping is definitely wrong

    I know it doesn't match Burnham's installation guide at all.  I've been debating whether to fix this summer or wait for a new boiler at some point down the road since its already been this way 20 years and seems to work without being noisy and it's not horribly expensive to operate.  But I don't know why the probe would trip only occasionally.  Like I said, I've only seen it do this once.  The old probe was the MM PS-801-24.  Maybe it happened and I never noticed.  Maybe this new probe is programmed to do it.  Maybe it was just a one-off thing for one reason or another.  Anyway - I'll keep an eye on it and post back if I notice anything else.