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Skimming - Keep temp at 180-200 degrees

So I am a novice boiler homeowner, but feel comfortable with a cold skim. The manual of my new gas-fired Carrier steam boiler indicates that I should fire up the burners to get the water to 180-200 degrees to skim, but avoid any steam creation. I saw similar recommendations on a wide variety of sites (including this one) for a proper skim.

My question - since I don't have a way of knowing the water temperature, what steps should I take to know the water is in that temperature range but without risk of creating steam?

The only "tools" I think I have to maintain water temp is the thermostat and the manual water fill (cold water).

Boiler info here: https://www.carrier.com/residential/en/us/products/boilers/bs2/
A lot of local folks (CO) were surprised that Carrier made boilers...


  • Jamie Hall
    Jamie Hall Member Posts: 22,916
    You can usually hear when the water is starting to boil. That's when you turn off the burner. The desired temperature range isn't terribly critical, so long as it isn't actually boiler -- and is very very hot.

    If you do have a thermometer which will read up there -- swipe your wife's candy thermometer? (on second though, go and get your own...) and just leave it's probe so that the water is going over it as it comes out (don't burn your hands -- and it doesn't have to be there all the time!).
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • pecmsg
    pecmsg Member Posts: 4,693
    Generally seeing mist or steam coming out of the opening is close enough 
    EBEBRATT-Ed Member Posts: 15,317
    @cold nights
    Start the boiler and check the steam line leaving the boiler, when you hand starts to burn (careful) it's steaming. Shut the burner off. Lift the lever on you safety valve to make sure there is no steam left in the boiler Open the skim port wide open (carefully). Adjust the make up water going into the boiler to just a trickle (the size of a lead pencil)
  • ratio
    ratio Member Posts: 3,605
    When I was skimming my church boiler, I picked up one of these & wired it in place of the on/off control (safeties were left in the control loop). I beat the end of a piece of 3/8 copper closed & slid the sensor down inside that, removed the relief valve & stuck it down into the water. I used it to both cook the minerals out with TSP & skim for hours at 200+° without worrying about making steam.

    I also welded a li'l weir across a nipple to stick in the skim valve. The whole thing was pretty much automated, I only had to check the bucket from time to time. Next time, I'm going to make a funnel with a piece of hose on the end to take it over to the drain.

    JUGHNE Member Posts: 11,021
    For skimming a system that had a boiler feed pump and no direct fast fill connection to the boiler itself, I used a double ended female hose to the boiler drain and to cold supply hose bib, (could be water heater drain or laundry bib).
    With boiler brought up to steaming, shut off boiler and pumps.
    Then add cold water very slowly thru the boiler drain to raise the water level up to the skim port. Let drain out very small stream until boiler water cool/cold.
    Drain down to operation level and fire boiler to drive off O2 gases.
    Repeat as needed.