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Not enough hot water

I have a friend who has an old cast iron steam boiler.  Running out of hot water.  I suggested Cleaning the coil like I always do with an acid pump and sizzle.  Hard water and all. He is going to put in a thermostatic mixing valve in when problem started not longer ago.  I saw boiler its aged close to 40 years has separated high and low limits switches. Boiler is older than triple aquastats.  I think sizzle through your coil w/ acid pump would be the route to go.. Anyone else have an opinion?? 
Mad Dog_2


  • Mattyplmbgandheating
    Mattyplmbgandheating Member Posts: 3
    edited March 5
    Here is pic of how old boiler and coil are. He hinks after all these thermostatic mixing valve will magically pull sediment outta coil 🤷🤷🤷
    Mad Dog_2
  • Mad Dog_2
    Mad Dog_2 Member Posts: 6,475
    The mixing valve is great to prevent scalding, but will only get clogged and slow flow worse.  Its cheap enough to just replace it.  Diversified Heat Transfer in NYC makes nice kits  mad 🐕 Dog  stop wasting your precious time Matthew   mad dog
  • MikeL_2
    MikeL_2 Member Posts: 471
    edited March 5
       We stopped using Sizzle over 30 years ago ( no Clobber, either). In my opinion, it's too dangerous to store, handle, and dispose of. The fumes are toxic, it's hard on the tools & pump, and, Sizzle can eat through tankless coils.
        We use Rydlyme by Apex Engineering. Safe to handle & store,  biodegradable, effective, and it can also be used safely on indirect water heaters, heat exchangers, and toilet bowl rim & siphon jets.....
  • Mattyplmbgandheating
    Mattyplmbgandheating Member Posts: 3
    Thanks guys!!
    EBEBRATT-Ed Member Posts: 14,543
    If he is not getting enough hot water the mixing valve (although every tankless coil should have one) will only reduce the hot water. But it is required to prevent scalding
  • MikeAmann
    MikeAmann Member Posts: 910
    How do you figure Ed?
    If you have 2 gallons of too hot water in the tankless coil and add cold water to that hot water to make 120 degree water at the taps, then you now have more than 2 gallons available to use.
  • Jamie Hall
    Jamie Hall Member Posts: 22,162
    Tankless water heaters and tankless coils (really rather different beasts) are rated differently from tank type hot water heaters. Tankless water heaters are rated in terms of the flow (gallons per minute) they can heat from the cold water temperature to the hot water temperature (typically 50 F to 120 F) on continuous firing. They have no storage, and are not designed for storage. If the flow rate is exceeded, what happens is they can't heat the water as hot -- and you get a cold shower. If a tankless water heater could be set at a higher temperature, you could increase the usable flow rate by mixing in some cold to bring the temperature down. Tankless coils in a boiler are somewhat similar, but they often do run at a much higher temperature, so a mixing valve not only increases the rate at which you can run hot enough water -- but is required to prevent scalding (there is a complication with tankless coils in a boiler: they do run out of hot water eventually, as usually the recovery rate of the boiler itself is too low --like a tank type unit).

    Tank type units are quite different. In them, the recovery rate of the burner or elements is much too low to be of use in any normal hot water flow situation. Rather the principle is that the hot water demand -- a shower, perhaps -- will be met by drawing already heated water from the volume of the tank, and replacing that over time by slowly heating up the cold water which came in to replace the hot. Here one can increase the apparent volume of the tank by running it hotter (there are other benefits, like no bacteria!) and mixing it down with some cold to get the flow required.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England