Cast Iron Pump for Hot Water Recirculation?

Discussion in 'Water Heater Forum, Tanks' started by SAS, Jul 6, 2014.

  1. SAS

    SAS Member

    Messages:
    117
    Location:
    Connecticut
    We have a hot water recirculation system in our new house that is working just fine. But we have been having some HVAC issues and a fellow who came by to give us an estimate on a new heat pump pointed to our hot water recirculation pump (Grundfos UPS 15 58FC) and told us that it was a code violation to use a cast iron pump in the domestic hot water system.

    Is that true? Beyond the code issue, is there any risk from it? If so, what is the risk? If it's just premature pump failure, I can easily wait for it to die. If it's going to cause a problem with the hot water heater or the water itself, I'll have to replace it. And in that case, what is my best bet for a replacement pump?

    Thanks for any help.
  2. If you have a cast iron pump and the cast iron is in direct contact with your potable water in hot water heater , then it will eventually make your water in the water heater brown or rusty,,,,

    we are speaking about a circulation pump for your hot water heater...??? correct..... it will work, and wont hurt anything but will turn the water rusty brown over time... which would not be good for your white whites in the laundry

    how long has it been like this??





    Terry likes this.
  3. SAS

    SAS Member

    Messages:
    117
    Location:
    Connecticut
    Thanks for the reply and information. I can't say how old the pump is, since we just bought the house. The hot water heater is fairly new (maybe 1-2 years) and it looks as if the recirculation pump and the expansion tank are also fairly new. Since I've started looking into this, I also discovered that the pump is installed incorrectly: according to the Grundfos Installation Manual, "Under no circumstances should the pump be installed with the
    shaft vertical or where the shaft falls below the horizontal plane," but this pump is installed with the shaft positioned vertically. Also the fittings that connect the CPVC to the flanges are labeled "for cold water only".

    There is a shut off valve before the pump ,a brass check valve after it, and another shot off valve after that. Since the pump has a built in check valve is there any harm in having both? There is another check valve by the tee to the cold water feed into the hot water heater. Is there anything else I should change out while I'm putting in a new pump?
  4. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,271
    Location:
    New England
    A CI pump works in a hydronic heating environment because whatever dissolved oxygen that is in the water gets 'used up' fairly quickly...IOW, it causes rust or corrosion of anything that can rust or corrode. After short order, unless there is a leak, the water becomes fairly inert which is why it works in a closed system like that. But, in potable water, there is a constant supply of dissolved gasses, and the corrosion and rusting will happen continually, leading to eventual, premature failure. This rust can cause stains over time in sinks, tubs, showers, etc, and isn't all that great for keeping your white clothes white (assuming you use any hot or warm water to wash them!).

    Throw in the fittings that are not allowed for hot water, the pump being installed incorrectly, and it would seem like it would be a good idea to fix those problems. Eventually, if the motor windings don't short out, it may still be turning, but the impeller will just be a shaft, and not move any water at all. Brass or SS pump is required with potable water, especially when you throw in heated water which speeds up deterioration of the CI parts.
  5. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,058
    Location:
    Cave Creek, Arizona
    Cast iron pumps in a domestic water system rust very quickly and usually "freeze up" when the parts join together.
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