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Cleaning Scale from A.O. Smith Vertex Hot Water Heater with Hydorchoric Acid?

I live by myself in a small 1 bedroom house over a 3 car garage in Northern Vermont and believe I have scaling issues in my propane fired A.O. Smith Vertex Hot Water Tank. I bought this tank specifically to use for both domestic hot water AND to heat my house using a plate heat exchanger with a closed loop to the radiant heat system. For the past 4 years the heating system has worked well except in the coldest of temperatures when it's calling for heat and I'm trying to take a shower!! I now have t'stat's on timers that shut down in the morning just before my shower and that makes it all work well!

Regretfully, I never put a whole house filter between my well and my hot water tank. As a result, I have slowly lost flow. I'm sure I have also lost flow due to scale build-up in the hot water tank.

This summer I installed a whole house filter... installed a soft water treatment tank... and flushed all the crap out of the system. In addition, I removed the drain valve on the hot water tank and created a "stand pipe" with 3/4" pipe so that I could take a funnel and fill the tank with Vinegar. (I could only fill it as high as the pressure valve at the top of the tank). I then let it sit for several days and a whole bunch of crud came out of the drain... it worked great and I was so hoping it had cured my issues of low flow!!

My cold water flow was 100% cured but not my hot water flow. I just replaced the mixing valve on the domestic side thinking that it may have scaled up due to my running the tank at 150F during the winter time and it indeed improved the flow considerably... but I wouldn't say 100%.

QUESTION: Since I live by myself... is there any harm in putting Nu-Calgon Liquid Scale Dissolver (hydrochoric acid) into my hot water tank and let it sit for 4-6 hours... and then flush-flush-flush the whole system out? Obviously there is the proper safety precautions of handling acid... but will this damage the internals of this Vertex Hot Water Heater? Reading the Nu-Calgon instructions makes it appear that I will be okay... but I wondered about the anode that I understand to be inside the tank.

Your timely response is GREATLY appreciated!


  • Ironman
    Ironman Member Posts: 7,379
    It's probably your dip tubes and piping that are scaled up to the point of restriction. If the actual tank was scaled that bad, you wouldn't be getting good heat transfer from the burner to the water and your flue temp would be elevated to the point of compromising the PVC vent.
    Think about what you're proposing: filling a domestic water heater with hydrochloric acid?
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • icesailor
    icesailor Member Posts: 7,265
    It would depend on the strength of the Nu-Calgon acid product. But if you used white vinegar before, use it some more. But you need a way to pump it into the cold until it comes out the hot. So that the complete tank is filled with vinegar.

    Have you ever had the water tested? Is the water crazy hard with really high dissolved solids? Do you have high iron? Some places in Vermont have a lot of iron in the soil. They mined Iron during the American Revolution to make Cannonballs around Bristol, VT. Iron is a form of hardness.

    If you're really handy and clever, it helps to use compressed air to blow air back and forth through the tank and HX to loosen up the crud. If Vinegar improved it, keep trying. I've cleaned many a coil with acid. Just thinking about using it makes my lower extremities pucker. If you really want to use regular acid, you really need a specific acid pump with vinyl hoses and connect the whole tank and HX from the pump in a bucket of acid, and the solution returning to the bucket. It will take some time. Not for the faint of heart.
  • MikeL_2
    MikeL_2 Member Posts: 494
    edited November 2014
    I recommend Rydlyme, manufactured by Apex Engineering. This biodegradable electrolyte, is safe to handle, and, very effective at dissolving mineral deposits. I've been using it to clean tanklesss coils and storage tanks for the past 30 years, and, I often save the used fluid to clean toilet bowl siphon and rim jets..........
  • RobG
    RobG Member Posts: 1,850
    Did you circulate the cleaner through the heat exchanger?
  • Tim Potter
    Tim Potter Member Posts: 273
    edited November 2014
    Another possibility, Here is what amtrol recommends for cleaning their Boilermate:


    used it on mine, great results.

    Notice its phosphoric acid & safe for use in ice makers not hydrochloric acid.

    Winter Park, CO & Arvada, CO
  • MikeL_2
    MikeL_2 Member Posts: 494
    Yes, I use a Nu - Calgon # 31 pump , the same pump I've used in the past with Hercules Sizzle. I have not used acid in at least 30 years ( including for drain cleaning ), and, when using Rydlyme, you can unplug the pump and let the coil or tank / exchanger soak idle without risk of overreaction.
  • TomS
    TomS Member Posts: 62
    I would never use Hydrochloric acid to clean up anything in a confined space as poisonous gases are often released. Here is a link about some farmers using it to clean a well screen.
  • cevhh
    cevhh Member Posts: 3

    Thanks for your help and coaching... I will ditch the hydrochoric acid and review both the Rydlyme and the Nu-Cal Liquid Ice Machine Cleaner to see which one is most easily available vs. cost.

    I so greatly appreciate your interest to help me out... will let you know how I make out!