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why my steam heat turns on when I use hot water

zahidscorp Member Posts: 1
Hi, I have oil funace steam heat. I turned off the thermostate and its prety hot in summer. My furnace gives me heat and hot water. My problem is that when I use hot water my cast iron radiators start heating up and works like I am using heat. what would be the problem? thanks for reading this question.


  • Jamie Hall
    Jamie Hall Member Posts: 19,156
    There should be an aquastat with a high limit on the boiler, which should turn off the burner when the water reaches about 180 and there's no call for house heating. Sounds like it's missing, not properly wired, or not working.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    EBEBRATT-Ed Member Posts: 12,162
    @zahidscorp ,

    tankless coils generally have poor capacity for heating domestic hot water. In order to get the most hot water possible the low limit aquastat temperature adjustment is usually raised=hotter boiler water= hotter domestic hot water. The problem is if it's raised too high the boiler could make steam and start heating the radiators. Check the aquastat setting it should be 180 or less. It is usually a rectangular control installed in the boiler water the gray cover maybe 1 1/2" wide x 8" long. Shut the power off take off the cover and look inside there is a wheel with temperature settings you can adjust. Or it could be a defective control or have sludge built up around the sensing bulb well.
  • newagedawn
    newagedawn Member Posts: 586
    can you post a pic of your system?
    "The bitter taste of a poor install lasts far longer than the JOY of the lowest price"