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Should system always be flushed before new install?

New Burnham ES2 being installed. I asked about flushing system (other bidders had mentioned it as being very important) and response was it isn't necessary due to: water draining out was discolored but no apparent solids, standard efficiency boiler won't have narrow channels that clog like a HE would, and the piping system is in parallel as opposed to monoflow so to flush the system each individual radiator would have to be disconnected and separately flushed.

Last winter a different contractor added sealant to the water to address a leak in the boiler. So in addition to any sludge buildup, oxygen had been introduced into the system via the leak (which never completely went away. I believe this was one of the reasons that contractor had recommended flushing.

The boiler is in position ready to be connected to the drained system. Thanks for any guidance.


  • delta T
    delta T Member Posts: 884
    Assuming you have cast iron radiators, I would absolutely have installed a magnetic separator and some boiler water treatment for this system. As far as actually power flushing the system, if it is an old converted gravity system or similar parallel piped system, it can be very difficult and labor intensive to effectively flush. In these cases I would at least flush until I got fairly clear water, and rely on the magnetic separator to mop up the rest over the course of a heating season or two.
  • hot_rod
    hot_rod Member Posts: 22,255
    To get particles or solids out, you need a fairly high flow rate, much more than you get from just opening the drain cock. The building water pressure offers a good flow, especially if you can isolate sections of the piping. You need about 5 fps to move a solid particle in a pipe or boiler HX.

    Running a cleaner first will help loosen, dislodge and scrub away the sealer you added.

    Yeah it will add hours of time to do a proper system flush, but it is highly recommended.

    When you split open the sections and look into disassembled components, you find what is lurking in your system.

    Thanks to Kevin and Andy for sending these discoveries.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream