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Weekly blow downs and make up water

Several discussions on boiler maintenance lately...

Does anyone have anecdotal evidence that boilers with float type low water cutoffs have shorter lifespans than probe type cutoff equipped boilers? 

I’m asking because I can’t figure out the functional difference between adding a gallon of water per week through replenishing blowdown water vs. any other leakage. 

If makeup water was really that bad wouldn’t we see the probe equipped boilers last much longer?  

I add a little more than a gallon of water a week to my big system (18 rads,  860sq ft) which must be the packing nuts leaking steam (wet returns are brand new).   The Big Mouth main vents also take some time to close once steam hits  but that can’t be a gallon a week loss. Maybe a few ounces.

It was concerning before I realized that my last boiler had weekly gallon size blow downs for 20 years and was fine (junked to convert to gas). 

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 15,415
    The functional difference for a weekly blowdown is that the water is boiled if not immediately, very soon after the water is blown down, and any oxygen in there is driven off.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Derheatmeister
    Derheatmeister Member Posts: 1,003
    edited February 19
    Frequently adding water to any system is not advisable..
    It will introduce Oxygen and Minerals which we all know are the cause of many issues.
    Blow downs are advisable but should not have to happen all of the time.
    I think you may be onto something regarding the Probe type vs the float type cutoff but it may be better to talk to someone that has experience with this and your system.
    My advise is to reduce some of the frequent replenishment of water by repairing the leaks on the stems and maybe reevaluating the Vents.
  • ethicalpaul
    ethicalpaul Member Posts: 2,798

    The functional difference for a weekly blowdown is that the water is boiled if not immediately, very soon after the water is blown down, and any oxygen in there is driven off.

    Well ok, but isn't it true that any makeup water (let's say in a leaky system with an autofeeder) is also immediately boiled? So how is it possible that a lot of makeup water can cause additional corrosion?

    But to the original poster, also keep your PH around 10 or 11 and that should greatly reduce corrosion.
    1 pipe Peerless 63-03L in Cedar Grove, NJ, coal > oil > NG
  • Jamie Hall
    Jamie Hall Member Posts: 15,415
    It's really a case of pick your poison. Yes, the additional water from blowdowns of a float type control is undesirable. But then, failure of the float type control due to getting stuck (either up or down) is undesirable (and yes, I've had it happen). But then failure of a probe type control because it's grubby or the electronics go paws up is undesirable.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 8,581
    I have seen many boilers dry fired because the LWCO didn't work. I have seen the electronic ones fail as well as the float type.

    No substitute for removing and cleaning on some sort of schedule.

    Do the float controls need to be blown down weekly as MM says? Maybe. You look at the water and blow it down take it apart after the first year and see what it looks like. Then you can adjust your schedule based on what you find.
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