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Indirect water heater tank back flow questions

aaronhl Member Posts: 3
Bought a house about 4 years ago with a 20 year old indirect water heater tank (boiler heats the coil).
It had a bunch of rusty sediment in it, which made the hot water dirty, so I flushed it several times.
Since then the hot water has been okay, but I've been noticing lately the COLD water quality is making the toilets and sinks stain. I have city water and I do not "think" my underground pipes are busted.
Would it be possible for the rusty indirect water heater tank to back flow causing the cold water supply to become rusty?


  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,833
    edited May 2020
    It may be a coincidence. Has the fire hydrants in your area been used? Was there any road work involving the water mains?

    Unlikely, but could you have forced contaminated water from the Indirect DHW tank backward into the cold line? What method did you use to "Flush" the DHW tank?


    Was the flushing process used able to shock the pipes and loosen sediment in your cold water service?
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • aaronhl
    aaronhl Member Posts: 3
    Thanks for your message
    The city flushes the hydrants every year and I haven seen any construction... But the toilets constantly stain

    Not quite sure I understand your question... I have a back flow preventer on the boiler supply and a shut off that is always closed.

    I do not have a back flow preventer in-line From the supply to the indirect heater tank.

    When flushing the tank, I let it drain out with the cold water supply shut off with the blow off valve open.

    My hot water gets really hot

    My water comes from a the cities 3 story large tank about 1/4 miles away...I‘m beginning to think that tank has rust in it

    Hopefully that info helps let me know if I could illustrate anything else
  • hot_rod
    hot_rod Member Posts: 22,122
    Your incoming water line, what is it, copper, galvanized, plastic?

    Fill a glass jar with cold water, let it set overnight see what settles

    Turbity goes up in springtime in some areas, a fine silica that gets into the water system, causes some brown coloring
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    EBEBRATT-Ed Member Posts: 15,517
    Ask your neighbors. Make sure your relief valve on the boiler is operational and check the boiler pressure S/B 12-15 psi.

    If the indirect coil leaks it will raise the boiler pressure and open the boiler relief valve.
  • aaronhl
    aaronhl Member Posts: 3
    Good info about the pressure increasing, that is def not the case.

    I actually have a problem keeping the boiler pressure around 15 during the winter. I usually have to add water to it it every couple months from the water supply. I think I have a leak in one of my zones due to it freezing up in the attic.

    I believe the underground water supply coming into my house through the foundation is galvanize because of the color of the pipe. It then goes to copper throughout the house.

  • hot_rod
    hot_rod Member Posts: 22,122
    How old is the home? If it has a galvanized water line, 20 years or more old, that could be the cause of the rust.
    Some of the new chemicals that public water providers use could be stripping that galvanized pipe and causing the rust.

    That is what allegedly happened in Flint, MI. When they changed water source the newer chemicals stripped all the biofilm form the piping and they were getting rusty waster everywhere in the system.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream