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water feeder & low watere cutoff

I have a low pressure steam boiler with a ITT M&M Uni-match Universal Water Feeder connecter to McDonald No. 67 Low water cutoff control.

I checked the gage glass and the water level was low so I pressed the manual feed and the water feeder would not shut off. I disconnected the water feeder and am using the bypass.

Last year before the heating season, I put new bellows in the no. 67 and it ran all season without a problem.

Do you thing the LWCO is stuck or the water feeder needs to be replaced.



  • bustoff315
    bustoff315 Member Posts: 26

    Was the water level low enough to activate the LWCO and shut the boiler off?  You would have to test voltage to see if the LWCO is sending power to the to the water feeder.  If it's not, it's likely the manual water feed switch got stuck after you pressed it.
  • Water Feeder & LWCO

    Thanks for your quick reply. The water level was low ~1/2 to 3/4 inches when normally it's 2 1/2 to 3  inches.

    In the past, I just tapped the LWCO with a hammer and the system return to normal. That is why I replaced the bellows - the old was corroded but not broken.

    I was just looking and took the cover off the LWCO 24volt control and I noticed that the probe should be inspected annually. I've never done this. We put the boiler in new about 10 years ago.

    To check the probe and also the bellows switch, I would have to drain the boiler.

    I don't have couplings isolating the water feeder, just on/off ball valves. So I would have to cut the pipe and install couplings.

    Is there any way I can isolate the problem?

    Three issues the water feeder, the LWCO and he 24 volt with probe.

    Thanks again.
  • bustoff315
    bustoff315 Member Posts: 26

    Disconnect the wire that goes to the W terminal on the water feeder. If the water feeder continues to operate then the problem is isolated to the feeder. That wire from the W terminal is connected to the #4 terminal on the 67 LWCO. The #4 should only be powered when the water level is low and the float inside the LWCO drops. When the boiler has enough water in it, the float is up and the switch powers the #1 (burner) terminal.
  • water feeder & low water cutoff


    Thanks for you help.

    I check the voltage from the lwco to the solenoid water feeder - it's zero - so I'm assuming the lwco with bellows is working properly. No electric to the water feeder - so no activation.

    The other Black wire to the feeder is active. I cannot trace this since it is integral with the boiler gas controls.

    I think the low water probe is the problem. I tested with the test button and get a yellow indicator. According to the directions in the cover the probe is probably grounded causing a false low water single.

    But, I pulled the contact on the probe and the supply(electric) is still going to the water feeder. By the way, with the probe supply off its connection I get a red light in the low water probe box which says "manually reset".

    Any thoughts?
  • bustoff315
    bustoff315 Member Posts: 26
    Dual LWCOs and a water feeder

    There is always power to the H terminal on the water feeder.  On a 24v water feeder it should come directly from the transformer.  That is so the manual water feed button will operate when you press it in. 

    I completely misread your post and thought you only had a M/M 67 LWCO.  What model internal probe LWCO do you have?  Does each LWCO send a wire to the water feeder "W" terminal?  I've yet to personally come across a setup like this. Pics would be great.

    When the water was originally low when you pressed in the manual feed, was the yellow low water light on?
  • water feeder & LWCO

    I've determined the water feeder is not the problem. If I turn on the valves through the WF - no water goes to the boiler. So it is operating correctly.

    The No 67 also appears to be working correctly. The 110V line from the 67 is not energized so the float is up and the switch is off.

    There are two black wired attached to the connector. The one that comes the cable that disappears into the furnace proper is hot. I connect this to the WF - it activates and water flows to the boiler.

    So, it looks like I have the No 67 low water float and a low water low water probe. Either one can activate the WF.

    The probe is a McDonnell (LWCO) 24V - Model No PS-802-RX2-25. The test button when pressed indicates "yellow" which per instructions inside the cover say that maybe the probe is scaled over and the probe grounded.

    I tried to test the probe with a multi meter. If I attach one end to the spade connection from the probe and the other to ground, A get single that their connected

    Can I assume from this that the probe is grounded and needs replacement?

    Again, thanks for you advice and help.

    PS: When I first purchased this house I hade to replace the boiler. The old one was oil fired - converted to  gas and on it's last leg. I had installed a Peerless cast iron unit  rated at 400,000 btu. Since I knew nothing about low pressure boilers I found Dan's book - The Lost Art of Steam Heating. The book and the wall have been a savior.
  • bustoff315
    bustoff315 Member Posts: 26
    PS-802 water feeder

    When you press the test button on the PS-802, a dull yellow light indicates there is enough water in the boiler, a bright yellow light indicates that the probe may need cleaning. 

    If you haven't already before this season I would drain some enough water out of the boiler (while the water is cold) and test both LWCOs to make sure they are both operating correctly.  While you have the boiler drained down it wouldn't be a bad idea to take the probe out and clean and rinse it off.  Do not use Teflon tape when you re-install the probe.  How old is the PS-802 probe feeder?
  • water feeder & low water cutoff

    Hate to say it but I have never removed the probe. I did not know until this recent problem - having just read the instructions after removing the cover.

    The whole set up is 15 years old.

    If the probe is not working would that account for a hot wire to the water feeder?

    Is there another thing I should check where the hot wire enters the boiler?

    Right now, I have the water feeder connected with the LWCO (bellows) .

    My thought is that their redundant right now and this should work until I drain the boiler and clear/clean the probe.

    As always, thanks for being there.

  • water feeder & low water cutoffg

    PS: it looks to me that the yellow light is bright.
  • water feeder & low water cutoffg

    PS: it looks to me that the yellow light is bright.
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