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LWCO maintenance question.

In other threads, it is suggested that the LWCO should be blown down on a weekly basis.

I have a hot water (not steam) system with am McDonnell & Miller RB-122-E LWCO in it.

The way they suggest installing it includes no facility for blowing it down, although water circulates past it whenever the boiler is firing. Furthermore, in the maintenance schedule of their instructions, it says:

Test the low water cut-off annually or more frequently (there is a button on the device for this).

Remove and inspect the self-cleaning probe every 5 years.

Replace the probe every 10 years.

Replace the low water cut-off every 15 years.

1.) Is there a significant difference between this unit and those used in steam systems? To clarify, I would not propose using this unit in a steam system, since it is not designed for such service.

2.) It seems to me that the labor costs of replacing the probe every 10 years would mean it would be cheaper in the long run to replace the whole unit every 10 years than doing the probe every 10 and the rest of the unit 5 years later. Right?


  • Tim McElwain
    Tim McElwain Member Posts: 4,588
    Float type

    LWCO versus Probe Type, both can be used on steam systems as the probe type simply uses a circuit to ground through the water to prove water level.

    Flushing a float type should be a weekly thing on a steam system to insure that the float stays free from any sludge build up and will not work. It should be flushed with the boiler running to insure that when it is flushed it shuts off the boiler.

    The probe types should follow the required maintenance of the manufacturer. It is obvious that on a forced hot water closed system we would not flush the system down as this would allow city water to enter the boiler and create a water in-balance eventually damaging the boiler.

    The newer types of probes which have a device attached for keeping the probe clean need serviced every 5 years or so depending on water quality. I would not replace them unless the diagnostics showed them faulty as for replacing the entire unit, not until it fails which could be 20 years or so.

    There may have been some early units which had quality issues and needed more service but most of the new ones are pretty good.
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