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Expansion tank rust and water quality

pete0007
pete0007 Member Posts: 6
in Gas Heating

Hello there, little bit of background and couple of questions. I have navien combo boiler, at the moment space heating side of it is heating the home with water to air heat exchanger and air handler. I'm extending this system for under floor heating and have it ready to hook up to existing space heating. I plan on draining the system and filling it with new liquid.

  1. Should I just use distilled water? I'll need about 10-12 gallons.
  2. Water in the system at the moment is light brown, seems like rust from the expansion tank. Is it time to replace the expansion tank? I was using soft water, could that be the cause of rust in the expansion tank? Would adding some kind of stabilizers help?

Thank you.

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 26,515

    What is the rest of the piping and the boiler made of? It could be rust from the expansion tank — but most tanks are lined, so that seems unlikely.

    However. If there is iron or steel or stainless steel and you are using softened water in the system — there's the problem. Softened water is surprisingly corrosive, particularly for stainless steel.

    If you are on municipal water, unless you are in an area with high chlorides,, that should be fine, but desionized water is better. Distilled isn't necessary, and it, too, is surprisingly corrosive.

    Unless there is a genuine risk of freezing, I'd use plain water, but there are some corrosion inhibitors which others may recommend.

    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • hot_rod
    hot_rod Member Posts: 25,918

    before you drain add a cleaner, run for a day then drain and flush. Check you homes water for at least hardness, TDS and chloride

    Your boiler manual will have a water quality spec for those levels. If it is out if wack bring in some water. Walmart and others sell ro water take a few 5 gallon jugs

    Really RO, destilled, deionized is all 90% pure water, just different methods are use to filter it. It is “hungry , low ph water. But it doesn’t stay that way for long. Once in the system it pulls ions from the metals and ph buffers up. But better to use an inhibitor for that snd protection for all the system components

    When all is filled and leak free add an inhibitor

    All the hydronic chemical companies sell two part easy to use dispenser cans now

    IMG_1208.jpeg
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • pete0007
    pete0007 Member Posts: 6

    Thank you both for your response.

    Most of the system is PEX-A or O2 barrier PEX. Only metal(Cu) is the Water to air heat exchanger, the heater itself and the expansion tank. I can see the connection to the expansion tank is the the darkest of all the PEX pipes.

    Our municipal water varies from a TDS of 100 on a good day to 1200 at its worst.

    So the advise seems to be

    • Check Hardness, TDS, PH and Cl of local water, dilute it with clean water if necessary.
    • Add Cleaner before draining and add an inhibitor during refill.

    Fernox seems to be a little hard to find. How good is Hercules seems to cost a little less too. Sentinel seems to be another one that is not inexpensive but a little more accessible.

    Any thoughts on the expansion tank replacement and one of the cleaner/inhibitor products?

    Thanks again for your help.

    SuperTech
  • pete0007
    pete0007 Member Posts: 6
    image.jpg

    Water requirements for Navien seems to be very permissive, I’m not complaining 😀Just not use soft water.

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