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McDONNELL & MILLER low water cut-off overfilling at power on

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bomyo
bomyo Member Posts: 5
edited January 2023 in Thermostats and Controls
I have a McDonnell & Miller low water cut-off on my Burnham steam boiler. It has been overfilling at first power on. It will flash the red light and fill the water when the main boiler switch is turned on. Once the power is on and it does its job. I didn't realize the problem until a few years after the installation. I could not find the manual for my unit. I saw 2 jumpers at the upper corner and would like to know if my issue is related to the jumper setting or the wiring. Picture attached.
Thank you




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  • Steamhead
    Steamhead Member Posts: 16,835
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    That type of LWCO does a self-test when powered up, part of which sends voltage to the feeder. It needs to be hooked up to a feeder that has a delay before it feeds. We like the Hydrolevel VXT where you can adjust the delay period.
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Consulting
    EdTheHeaterManbomyo
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,834
    edited January 2023
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    The solenoid valve you shoe in the picture in picture is a instant on valve. as soon as there is power, the valve opens to let water in. By changing it to something like a Hydrolevel VXT where you can adjust the delay period, the self test on your LWCO will not be on long enough to add unwanted water. I believe it you connect those two terminals in the red box, for a second or so, (jumper then out for a second) that will send your LWCO into test mode. Just what you don't want to happen.
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
    bomyo
  • bomyo
    bomyo Member Posts: 5
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    @Steamhead, @EdTheHeaterMan Thank you both so much for the prompt reply. I noticed my unusual setup with a solenoid feeder after watching a lot of youtube boiler videos. I was hoping to find the delay dip switches in LWCO box which has the mark "M2". I will consider replacing solenoid with Hydrolevel VXT.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,834
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    There may be a simpler solution. What is the model number of your solenoid valve. Perhaps the manufacturer makes a time delay solenoid coil for that valve. 30 second delay should be more than enough.
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • bomyo
    bomyo Member Posts: 5
    edited January 2023
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    It is Parker GP400. I am thinking about using Adjustable Time Delay - Delay on Make - 6 sec to 8 min by ICM . It should take care of my issue. Thanks





  • bomyo
    bomyo Member Posts: 5
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    Delay-on-make switch was installed with 30s delay. It turns out perfect quick & dirty solution for my issue. I might have to increase the delay for the condensate return. The switch also fits inside LWCO. Thank you all..

  • exqheat
    exqheat Member Posts: 185
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    you may wish to adjust your water supply valve for rate of water in. Remember condensate is on the way back. That can cause a water level rise. A slower feed rate can meet the condensate return. Test for proper level.
    John Cockerill Exquisite Heat www.exqheat.com Precisions boiler control from indoor reset.
    bomyo
  • bomyo
    bomyo Member Posts: 5
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    Great tip. Thanks.. @exqheat . The water level has been perfect so far. I will try adjusting the rate of flow using the supply manual valve if I have an over-fill issue.

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