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Draining a steam boiler

I am experiencing some surging and know that it’s time to skim the boiler. We had some pipes replaced and the plumbers didn’t skim the boiler afterwards. I read on the forum the tips to skim effectively and the first recommended step was to completely drain the boiler. Assuming the broiler has cooled down appropriately is there any risk to just using the drain valve to remove as much water and impurities as possible?


  • Jamie Hall
    Jamie Hall Member Posts: 23,270
    No -- assuming the boiler has cooled down. ;Really cool. Which, in the winter time, you may not really want to do, perhaps. But drain and refill is a recommended first step -- no a mandatory one, and in fact that and skimming do two very different things. So if you like you can go ahead and skim anyway, and keep the house warm too!
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • KC_Jones
    KC_Jones Member Posts: 5,736
    I would not drain it. In my minds eye, the oils are on the surface, so draining will allow them to cling to the surface of the heat exchanger as the water recedes, then when you fill it up, the oils (since they don't mix with water) may just stay there for a while. When you then skim, you may not get it all, and have to come back later for another try as the oils work back to the surface again.
    2014 Weil Mclain EG-40
    EcoSteam ES-20 Advanced Boiler Control
    Boiler pictures updated 2/21/15
  • ethicalpaul
    ethicalpaul Member Posts: 5,701
    I would always skim first. You can slowly (skimming requires this anyway) add water to a hot boiler without fear of cracking it. Then as you skim, it will cool the boiler over a couple hours. Then you can drain and refill at that time if you wish, although the same benefit would probably occur from just draining however much you need to in order to get the water back down to the normal level.
    NJ Steam Homeowner. See my sight glass boiler videos: https://bit.ly/3sZW1el