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Puzzler: Condensate Return Leak, LWCO, Auto Feeder

Looking for some thoughts from the wise people

here.  We have determined that there is probably a leak in our buried

condensate return piping, and I'm trying to sort out if our float-type

LWCO may also be malfunctioning.

My system: HB Smith 2500L

steam boiler with domestic hot water coil.  Runs on a Heat-timer

EPU-CH.  McDonnell & Miller 67 float LWCO with McDonnell &

Miller 101-A water feeder.  McDonnell & Miller probe LWCO with

automatic reset, just below the bottom level of the sight glass. 

Hartford loop an inch or two below the probe LWCO (seems a bit lower

than usual).

Symptoms: Waking in the morning with no heat

or hot water.  This only happens when night temperature does not call

for heat and the system is idle through the night.  I check the boiler

and there is no water visible in the sight glass, the red light is

blinking on the probe LWCO.  I fill the boiler manually by pushing the

button on the water feeder and as soon as the level reaches the probe,

the burner fires up.  This takes about 2 or 3 minutes, and after another

2 or 3 minutes the water level is nearly at the "normal" line.  After

this the system runs normally as long as the Heat-timer calls for heat

and cycles steam once per hour.  I have put the Heat-timer in summer

mode and observed that the water level dropped about 2" over a 2 hour


Hypothesis #1: Water is slowly leaking from the

system and the float LWCO is sticking and not signaling the water feeder

to work.  Water continues to drain and the probe LWCO eventually shuts

the system down.  I like this hypothesis because the system seemed to

produce hot water fine for the summer and our leak is only now being

exposed because the LWCO is malfunctioning and not turning on the water

feeder.  The only reason I am in doubt is that everything still runs ok

as long as there is a call for heat.  We know there is a leak, so at

some point the float LWCO must be triggering the water feeder.  Is it

possible that the flow of water through the return piping during steam

production slows the leak enough to not require makeup water?  Or maybe

just the way water is moving through the system prevents the float from

sticking?  Also note: when the system is producing heat, opening the

blowdown valve on the float LWCO does actually trigger the water feeder.


#2: At some point during the night, water leaks quickly from the

system.  The float LWCO signals the water feeder to turn on, but it

cannot keep up, and eventually the float LWCO turns everything off,

including the water feeder.  Water level continues to drop until the

probe LWCO also activates (Do these LWCOs turn off the water feeder if

the cutoff water level is reached?).  I have doubts about this

hypothesis as well because I would think that the float LWCO would need

to be reset by bringing the water level back to near normal before the

system would turn on again.  As I said before, the system turns back on

as soon as water reaches the probe LWCO, which is well below the float


Thank you all for reading and I hope you can help me solve this puzzler.


  • ALIGAALIGA Member Posts: 194
    I would start by fixing the leak

    And then You can monitor the feeder
  • srejasreja Member Posts: 168
    re: uzzler: Condensate Return Leak, LWCO, Auto Feeder

    I'm just an amateur so take my thoughts with a grain of thought.

    I too would guess that the problem is the main LWCO/feeder switch getting stuck and unstuck -- we recently had that happen to us.  (ps. A quick fix to that stuck float valve was a hard punch to the LWCO).

    We also have a buried return leak that is impractical to fix, which indirectly causes more fresh water and thus rust in the water.

    I would suggest a first step of installing a new water feeder that measures the amount of fresh water fed into the system.  There is a VXT model that it mentioned on the forum a lot that works fairly well.

    That's what we installed and it is absolutely essential to understanding the nature of the water loss.  It will let you see how much water you are losing and when.

    With that information you can both diagnose how bad your leak is, and when the LWCO is calling for water.

    As soon as you conclude that it's unlikely that your system is simply calling for so much water that its purposefully shutting down the boiler, and you conclude that the LWCO float is getting stuck in some fashion, i would replace (or clean?) that LWCO float switch.  I get nervous about relying on the backup LWCO so yeah, if in doubt i'd probably replace the LWCO float/feeder sooner rather than later.
  • Jamie HallJamie Hall Member Posts: 6,708
    Seems to me

    that something is slightly amiss with the controls (as well as the leak, patience).  In my view, either low water cut off should shut off the system, and it shouldn't run at all until both are happy.  The behaviour you describe, where it will turn on when the probe type unit is satisfied, even though the float unit isn't, and the water feeder doesn't activate automatically under those conditions, suggests very strongly that the float unit isn't working properly.

    It is possible that the vibration of the boiler firing may be enough to allow the float unit to operate properly and activate the feeder, and that the leak is enough so that at night when the boiler isn't firing the water level drops below both LWCOs (the float unit having hung up) and shuts the system down.

    They can be cleaned (you do flush it once a week or two, don't you?) but once they start hanging up it is -- in my humble opinion -- better to replace them.  This is a safety device, after all...

    Now that leak.  2 inches in 2 hours is wildly excessive.  Even if you get things fixed so that the boiler will run, that much fresh water is going to corrode that boiler and give you more, and more expensive, problems.  Find it and fix it.

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-McClain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • zwiegandzwiegand Member Posts: 5
    edited December 2013
    Replace LWCO, Install Meter

    Thanks to those who have commented so far.  The consensus seems to

    be that the float LWCO is malfunctioning.  We are definitely planning to

    find and fix our leak, but it will take time because our return pipes

    are buried in the basement of a commercial space that we do not own. 

    Anyway, I think our immediate plan should be to replace the float LWCO

    and to install a meter on the feed line.  Any thoughts on whether the

    meter should be upstream or downstream of the feeder?  In our case it

    would be much, much simpler to install it on the output side.

    Thanks again for the help everyone!
  • RreyRrey Member Posts: 18
    Test to be sure

    Test the return.

    Any time I suspect a return leak, i perform the following test:

    Cut the return loose on each side of the point were it disappears into the floor (Yes, I know, it's a pain bc it's iron piping, so you may have to need to add a cpl of unions and replace back to the next fitting, if you don't have a threader)

    Try to do it at roughly the same height on each side.

    Fill the return with water and monitor it for bit and see if the water level goes down.

    This will confirm a leak beyond any doubt.
  • Greetings from long ago and not so far away

    Has that lobby return leak got worse, or is it difficult to tell?

    Maybe it should be on your New Years resolution to do some repiping!

    Let's start a new thread on that.--NBC
  • srejasreja Member Posts: 168
    re: test

    Thanks for that testing advice -- that's actually a pretty good idea that could come in handy..
  • RJRJ Member Posts: 484

    lwco can be taken apart and cleaned, the sa101 has a strainer that should be cleaned or replaced at least every 6 months, a plugged up lwco could be part of the problem as others have said 
This discussion has been closed.


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